Hey, I am in midstate NY. I do not usually see volvo's of that vintage in any of the boneyards, but I will keep my eyes open.
It sounds like the door hole size is different? Are yours more similiar to the 140 series then? Is there any way you can adapt the later style without any major hacking? The later series is easily obtainable and you could even then adapt power locks, if you don't already have them, and then install a keyless entry system! Someone who lives in a less rust prone state should be able to obtain your vintage locks from a pick-and-pull for a very small amount of money and I hope they help you out!
There are some other sources around up here that would take me awhile to track down; if you don't get helped by anyone you can email me and I will try to do something for you... it would take awhile though...
Good luck