Forum members are giving you the std avenues for new wheels, so here are some suggestions for used:
Have you looked in the forum classifieds? A quick check found a set in LA.
http://986forum.com/forums/showthread.php?t=11328
Also, not up on my CA geography but if you live in the greater LA area, LA Dismantlers may have something. I've never had much luck communicating with them but maybe they don't want to deal with me since I'm in the middle of the US. You may have better luck since you're a local.
You haven't said why you are looking - are your old wheels beat up, looking for track day wheels, wanting to upgrade from 17's, etc. Giving us a little more info would help narrow down the choices. Also, what year is your Box?
+1 on jwilson95's comment. Inexpensive and Porsche wheels are mutually exclusive. Be prepared to spend some bucks.