You can buy them used or new in various kind of servers.
> How many of those who have/can have it are running Illumos and are putting money/time in it?
Dunno, I'm not really a Solaris guy. I use Solaris as a hypervisor for Linux and BSD LDOMs.
> And more importantly what's the outlook for SPARC?
Well, you could make the very same argument about Illumos. The Python developers wanted to drop support for Solaris already and OpenJDK upstream did actually drop it.