You can find ACT mags, original Canadian mags, MBX 140's for Para, SPS mags, new Remington mags for 9mm. No, the Mec Gar mags and TF basepads will not work, nor on Canadian mags in a magwell. Base pads are an issue for sure. You can find Para plastic plus two's that will work, look at the used boards for Dawson's. I am sure Dawson would do a limited run it there were an order large enough but that would require someone to spearhead it.
You can also have your gun fitted to take STI mags too.