I have purchased AMA numbers, and other graphics from Bill Fulmer http://www.customcutgrafix.com
Copied from Bill's site:
General Rule #6 of the AMA SAFETY CODE states, in part, "I will not fly my model unless it is identified with my name and address or AMA number, on or in the model." The validity of your AMA insurance may be at risk if General Rule #6 is not adhered to... Placing your AMA number on your airplane meets this important safety requirement.
It is NOT necessary that you preface your AMA number with "AMA". Rather, you may use the number alone, or with any combination of your choice of letters as long as the NUMBER is complete. Also, "Celebrity" numbers are available from the AMA..
To assist you in easily complying with AMA General Rule #6, I offer (10) 3/4" or 1" Names OR AMA Numbers (or a combination therof) in the single font and color of your choice for $12.00. (Metallic Gold or Silver $2.00 additional).
This offer is quite flexible and if you have a special requirement, email me and we can work out the details.
Prior to finding Bill's link on Bruce Tharpe's site I had some AMA numbers cut at the local "Fast Signs" store and they charged about 50 cents per letter or number.