Good Evening Tim,
this got me thinking, as I had exactly the same problem last summer. after a long session working the key around hoping not to break it off in the lock I did get it out in the end. In my case though it wasn't wear (the worn pins and springs had been replaced and matched to the key when my dad restored the car) but it had been lubricated with something that had gummed up a bit so a clean and lube with a little dry white grease/PTFE fixed it.
No problems at all since then. Although I have read that locks should not be lubricated at all, it worked for me.
Sorry that doesn't help you much with your specific question! Anyway - after a bit of googling I did find this lot who offer to make a lock fit a key, rather than the other way round, and seem to be car friendly.
I think to do this they would need to be able to match the pins to the key profile, so maybe they are worth a call if you haven't already.
Good luck.
www.cooperkeys.co.uk/page6.html