Summit actually has a listing on one, and a place I found online called AAA Marine Wholesale has the base in stock for 10 bucks cheaper. I dont know if I like ordering from an unkown supplier though...
AAA Marine is very reputable. I have bought from them myself. BUT, wherever you decide to get it from here's the deal....make SURE they have it in stock. SInce the old man Offenhauser died, quantity AND quality has dropped off dramatically....in fact, I am not sure they are even still producing. Just a bit of advice..