The short answer is: THERE IS NONE!
A quick Google search of the words "Haviland Coat of Arms" or "de Havilland Coat of Arms" will probably render merchants all selling the same image (with a few variations in the art work). It will consist of a silver shield with three black triple-towered castles, and a crest consisting of a helm, a crown on top of the helm, and a triple-towered castle on top of the crown.
Don't be fooled. That image does not belong to the Haviland or de Havilland surname, nor to all the descendants of a de Havilland ancestor, even if they prove that descent. The reason is because English Coats-of-Arms such as this bearing were granted to, or inherited by, an individual, and can only be passed down from eldest son to eldest son in that exact form.
This achievement was owned by a de Havilland man from one branch of the family and passed down through the eldest males of his line. (We are not yet sure to whom this particular bearing was granted, or who inherited it, but you can find some similar bearings in our de Havilland Bearings article.) The likelihood that you have the right to bear these arms, according to English custom, is extraordinarily small. (In fact, you'd probably know it if you were.)
In English and Scottish Heraldry only the eldest son has a right to the original arms of his father, but his younger brothers have a right to a slightly changed (or "differenced") version of the arms, and those can be be passed down through their male lines as well.
Therefore, there are many variations of this Coat-of-Arms, owned by de Havilland men throughout the years. The granting of these arms was regulated, and in England and Scotland it still is.
Nevertheless, this image is mass produced and sold by merchants generically under the false pretense that it belongs to "the Haviland family." This lie has led to a wide misconception amongst Americans that they can simply buy "the" Coat-of-Arms that represents their surname and hang it proudly on their wall as if it's a legitimate bearing.
There was no such thing as a "surname" Coat-of-Arms in traditional English Heraldry. Therefore, buying a Coat-of-Arms this way pays no respect to the rules of the Heraldic College. The merchants who perpetuate these images did not likely research your branch of the family and prove if you actually have the Heraldic right to bear that Coat-of-Arms on your wall, or on your coffee mug, or on a flag or bumper sticker or anywhere else. They are just selling art and misleading you as to what it really is.
If you just want the work of art, nobody will trouble you about it. The United States of America does not legally or constitutionally recognize Heraldic Armory. Even in England this image has been used for commercial embellishment, such as on the signpost of the De Havilland Arms pub in Hampshire, England:
This particular image probably is in the public domain and not protected by the College of Arms.
Some bearings are officially granted to companies and countries, but in medieval England, from which the de Havilland family hails, the Coat-of-Arms belonged only to a man, granted to him by a ruling monarch. If anyone else bore the same Arms without entitlement it was effectively identity theft, and punishable by law. To use an American analogy, imagine if someone took your Social Security Number and posted their name on it and presented it to the authorities as theirs.
Now all this might sound like bad news, but if you want a real Coat-of-Arms there is still hope. It is possible to request one to be officially designed specifically for you by the Heralds of England (the College of Arms). To do this, you have to prove your great grandparent's descent from a British subject. It doesn't even need to be from your paternal genealogy (male to male to male, etc). If you provide the proper documentary evidence that proves you descend from a British subject on some branch, the Heralds will work with you on designing a Coat-of-Arms for you and registering it. No, you aren't being granted the arms by a ruling monarch, like Armigerous Bearers in the United Kingdom, but this is as close as you're going to get!
You can then recognize Heraldic tradition and pass it down to your eldest son, and difference it (perhaps using the rules of cadency) for your other sons.
This effort is a lot of hard work, and it can be costly. There is a cheaper route: which is to just create a fictional Coat-of-Arms. You can hire a Heraldic artist to paint it for you, or you can even assemble one using Photoshop with elements you can find online. Just remember that the resulting Coat-of-Arms wouldn't be a real one. It may break Heraldic rules, even in how the art is drawn, and of course it won't be registered. You'd be simply creating a logo that represents you or your immediate family, that is styled like a Coat-of-Arms. But if you go this route, be honest with people about what it is.
But imagine having a real Coat-of-Arms, registered with the Heralds! How cool would that be?
To explore this opportunity, a good company to work with is Achievements. They will help you research your genealogy and advise you if you have any heritable right to bear a particular Coat-of-Arms, and if not, they will help you prove (if possible) descent from an English subject (hopefully from an Armigerous Bearer) and then work with you to design a great Coat-of-Arms and register it with the Heralds of England!