I've just realised I've made this whole site, and not once mentioned how to get a PowerPC Mac. PRETTY SILLY OF ME, but here you go in no particular order.
In all cases make sure you know what the person is selling you because the seller usually doesn't know what it really is that they are selling, try to get models numbers and then find the exact model on www.EveryMac.com
to make sure that you are getting what you're paying for.
Ebay is your best option if your looking for a top of the line PPC Mac since there are so many for sell and can be shipped everywhere it's really up to you.
Craigslist > For Sale > Computers
This option is usually a lot cheaper since you pick up the computer locally, but you get a vary narrow selection, if any at all of what type of PPC Mac you can get.
Those are your best bets for actually finding, and buying a PowerPC Mac as far as specs go the more "Mhz" the better, try to get one with at least 1gb of ram. And you might have to reinstall the os / install a updated version so here's links to which ever one you would prefer all though I don't recommend going any lower than tiger, unless your on a 500mhz or less G3
Oldest to Newest
Only download from the torrent if you have previously purchased he software.
Mac OS 9.2.2
Mac OS X 10.3 Panther
Mac OS X 10.4 Tiger
Mac OS X 10.5 Leopard