http://www.foxindustries.com/this is the one i use .
42.8mm is the dia. for golfballs . Ken is the guy i talked to .. he's happy to sell as cannonballs , he's a cannon lover .
the price is $1.50 ea. for 50 , with shipping to me in longmont colo. they charge @30bucks so i just called it 2 dollars per ball .
there are mant differant sizes . the one little thing to remember is that if you ask for a ball in inches ,they may or may not have it . BUT have some mm sizes that will work handy because they list the inches and the mm balls seperatly and might have what you need in the mm sized balls .
42.8mm for gb guns
hope that helps gary
i dont think theyd mind being a sponser ....if they got some orders ........i ran it by them once ......