Pretty good actually, Kilsyth has (had?) A P80 down there, they had 2 actually until recently, usually a fair pile of 850's, 700/900 series cars and a few 200's around as well. Think I've even seen a few 440's down there. I would say out of experience PAP Kilsyth is best for the older Volvos they usually have a few around. Campbellfield is better for the newer Volvos it seems, they had a P2 V70 as well the other day they might even still have it, it was basically a goner though, completely stripped, had a P80 as well, nice 850 and a few S40's. Of course this can change.
Pick-A-Part for the Melbourne locations have a website which shows what cars are where, its updated and is usually pretty accurate:
Imlachs in Springvale is basically Pick-A-Part but not owned by them, they have a few Volvos as well usually but no specifics or website like PAP does.