Well, I can say the UX Gauntlet mags won't work - too thick. Won't even be able to sand down the mag back to make it thin enough. Other than that, I believe it would have. Beeman 1359 25cal mag is right at 0.585" thick. Thickness varies up to about 0.592" as I move the caliper around checking thickness everywhere. Thinnest measurement I got as the 0.585".
Is there somewhere that has a variety of magazine with sizes that I can check to see if I can find alternative? No idea why these appear to be impossible to find at this point.
I finally found spare mags for the .25 caliber on ebay. Shipped price is same as Beeman would have charged. But Beeman doesn't even list that rifle in that caliber or the mags anymore - so no idea what's going on with that.