"There are also some other Tropic 12's available on Ebay, but they seem to be a hit and miss when it comes to shape and size."
True.
GS and Sternkreuz brands are usually Ok.
From USA supply houses...Star Time generics always fit and Clark's have been good too.
I have used a few GS PA 459-47 with good luck, do not know what the difference is between PA 459-47 and PA 459-57A.
Correction: I should have said: "I have used a few GS PA 459-37 with good luck..."
Have also sanded the sharp edge down a little bit on later style number 22 types but this only smoothes the top edge down, the flat sidewall remains. It looked a little better (to me) though. I mounted the case in a lathe with the crystal on it (no bezel), spun the case and sanded the edge, then polished it smooth like original. Sanding by hand may not give good results.
If the crystal is not tight enough to stay on the case you have to use a bezel to hold it on and I have an old ratty bezel for that.
I looked at a new Sternkreuz tropic 11 and it has a beveled top edge, part number XS 292.470 on the package. A Sternkreuz tropic 12 has a similar top edge and the p/n is XS 293.156 with 11 printed on the same line as the p/n but off at the edge of the envelope. Maybe it means it will work for 12 and 11?? Anyway, the beveled edge is not as sharply pronounced as genuine.
Checked one from ST and it has the sharp top edge, p/n RCC 12...it looks like the later genuine models.
Looked at one in a white envelope with a blue frame labled 'watch parts' across the top and do not know where it came from but it has a rounded top edge and it has p/n 5500 on it. You might spot one on eBay but I would not pay more than $6 or $8 for it with free shp.
Looked at a new genuine rlx 25-22 and it looks exactly like the ST RCC 12...hard to tell for sure because it is sealed in a plastic envelope.
My advice is not to waste $$ on a genuine crystal on watch projects.
Why not?
Because a cracked $100 crystal is worth exactly the same as a cracked $12 crystal. Ha!