The correct snap caps will depend on the caliber you need. Offhand, I can think of the following .32 caliber cartridges that were chambered in revolvers:
.32 Rimfire short
.32 Rimfire long
.32 Short Colt
.32 Long Colt
.32 Colt New Police
.32 S&W
.32 S&W Long
.32 H&R Magnum
.327 Federal Magnum
.32 Colt New Police is a .32 S&W load with a flat nose bullet, and for all intents and purposes can be considered interchangeable.
The .32 S&W, .32 S&W long, .32 H&R Magnum and .327 magnum share the same cartridge diameter, but differ in length(much like the .38 Long Colt, .38 Special, and .357 Magnum series). Ammunition, and by extension fired brass are relatively easy to find for these. I typically make my own snap caps out of spent cartridges from which I remove the primer and fill the primer pocket with hot glue to cushion the firing pin. A Zoom also makes snap caps for all of the calibers in this series except for .327 Magnum, although the .32 S&W Short are basically universal for any revolver firing any of the calibers in this series.
The .32 Rimfire series cartridges are the same diameter as .32 Colt(long and short) although the Colt cartridges are centerfire. Rimfire cartridges are unavailable aside from old stock, and the .32 Colt are close to being unavailable. The cartridge diameter is considerably smaller than the .32 S&W series cartridges, so nothing for these will be compatible. If your revolver is in one of these calibers, I'm afraid that you're basically out of luck.