Most any place that sells Crescent Forge wear parts can get them and most likely will have them if they're a dealer that's worth their salt. On my 588,there are a bunch of other brands that used those same Oliver bottoms. I always take an old one with me,whatever part I'm looking for. If the Oliver bin happens to be empty,I start matching them up. Case,Ford,I'm wracking my brain right now to remember another one,but it's a newer company like Knvernland or something. Maybe that's not it,seems like it started with an M,but I'm having a brain fart.
Bottom line,I wouldn't worry about availability in the least.