> where you can find SPARC systems

In case by "find" you mean "where are SPARCs still being used"... It is something of a niche, but all our missions in the European Space Agency use LEON processors; a design based on SPARC [1].

And since you mentioned OSes, usually it is either bare-metal stuff or RTEMS [2].

[1] https://en.wikipedia.org/wiki/LEON [2] https://www.rtems.org/