There is no such thing as a ‘coat of arms for a surname’. Many people of the same surname will often be entitled to completely different coats of arms, (notice the different Coat of Arms I have found for Thompson) and many of that surname will be entitled to no coat of arms at all. Coats of arms belong to individuals. For any person to have a right to a coat of arms they must either have had it granted to them or be descended in the legitimate male line from a person to whom arms were granted or confirmed in the past.
For more information on Coat of Arms, check out http://www.college-of-arms.gov.uk/
So until you can get your own Coat of Arms, enjoy these that I have found from different places on the internet: