I'd start taking up a collection from fellow brickboarders... I'm sure we all have a few old keys laying about. Surely someone has one that will work. All them old locks have been around for a while, and are well worn often enough to accept any old Volvo key.

I'll look around and see what I can scare up.

In the mean time though...go with the locksmith to just pick the lock so you can push the button to get teh tumbler assembly out. At least you'll still have it in case you find the right key someday. Or, maybe you can still buy just the key and tumbler assembly from Volvo...

And...in the mean time even before that... you could leave the whole thing in place, and buy a cheap coil, and a cheap ignition switch (which you can hide under the dash to keep the stock look), and bypass both the original coil and switch....but leaving it in place for when you find that key. That would probably be cheapest, and effective from a preservation standpoint.

The original ignition/coil parts are getting few and far between... I wouldn't go cutting/destroying any parts...

Good luck!
-Matt