I looked and shopped web sites for a couple of years off and on. Just do a Google search for volvo 1800 and you will get tons of sites. Look locally if your city, or nearest big city has a "Craiglist". Also, talk with volvo shops in the area. Over the last couple of years I'd say they have appreciated into the $6 to 10k ball field, for a nice one with no or little rust. Try and look for cars originating from the west coast or drier states like florida, california, texas, arizona, etc. I found a 65 1800S from Texas and had spent the last 7 years in dry eastern oregon with very minimal rust. They are out there but you have to give yourself time and do the research. Definitely have a good volvo mechanic check it out before dropping $$$. Good luck!
65 1800S 120K
89 745GL 175K
90 244DL 106K