Long before you worry about a source of cyanide, you should research local regulations to insure that you can, indeed, use it legally. I expect you won't be able to. Since 9/11 I expect the noose has been tightened extensively. It was difficult to procure before that date.
Sounds like you know and understand chemistry ----so maybe the cautions aren't important to you. It is important, however, that cyanide should not go lower than 9½ pH in order to remain safe.
Cyanide is used extensively in the plating industry. It has been, in the past, purchased from any of the normal chemical supply houses, assuming you had the proper credentials. It is (was) available in 100 and 200 pound kegs, but regulations may make it impossible for you to acquire.
Harold