I have a Marlin 1892 in .32 Long Colt made between 1905 and 1908, dating it from its features.
The last .32 Long Colt cartridges were made in the late 1970s or early 1980s. I believe, Remington was the last maker. An occasional green and yellow Remington box is found at gun shows.
A co-worker just found a full box of Winchester 1970s .32 Long Colt at a gun show here in Utah. He picked it up for $25, knowing I shot this caliber.
Winchester still makes .32 Short Colt ammo on occasion, and it works in revolvers and rifles. My Marlin 92 cycles .32 Short Colt ammo just fine, but others with Marlin 92s report it doesn't. I suspect it depends upon how much wear the rifle's action has.
To my knowledge, Winchester is the ONLY manufacturer of .32 Short Colt ammo in the world. It's feast or famine finding the Winchester cartridges; right now we're in famine. I've been all over the internet and didn't find anyone who had boxes. They're all backordered, though one site said it expected delivery in early January 2012.
The Winchester .32 Short Colt stock number is X325CP. The lead, roundnosed, heeled bullet is 80 grs. Velocity is listed at 745 fps from a 4-inch revolver barrel. In a rifle with its longer barrel, velocity would be a little higher, perhaps 900 fps.
Winchester does not sell ammunition directly, you have to purchase from a dealer who orders from Winchester.
Boxes of 50 or cases of 500 cartridges (10 boxes) are listed in Winchester’s website, and newly made empty .32 Short Colt cases are readily available on the net.
If you find ammo, save your empty cases, especially for the .32 Long Colt. You may wish to try reloading later.
I've been reloading for the .32 Long Colt for about 12 years. Search the internet under my name (Gatofeo) and you'll find a ton of info on reloading, and the Marlin 92.