You can still buy StormC 4, although I don't think it will run fully on an unmodified 68000 system. StormC 3 is on Amiga Developer CD 2.1, which is still available from multiple vendors.
If you're really going to write software for classics, I'd recommend vasm and vbcc. They're still updated and supported by Frank Wille (phx), and you can contact him for Kickstart 1.2+ compatible startup files. The C library isn't 100% complete, but it can supplemented somewhat by Frank's PosixLib, available from Aminet.
The community support for SAS/C should still be rather good, even if the product hasn't been updated in years.