Unlocking window stay locks

BayTrees

Our lovely new home has aging wooden windows at the back, all of which need at least some TLC. Listed building so we want to repair rather than replace like for like. All the downstairs windows open outwards and have stay bars along the bottom to fix them in different positions. Unfortunately these are all fastened with stay locks and we have no corresponding keys. My guess is this goes back to the owners before last as all the windows have been painted shut on the outside and have obviously not been opened for some time. My only idea at the moment is to buy a sample of every stay lock I can find online and see if any keys fit. We can't shift the windows at all so can't take them off at the hinges or remove the locks. Has anyone got any advice or better ideas? I would LOVE to be able to open some windows.

SailorSam

Window lock keys are usually pretty standard, a bit like a star key.
If it looks from the outside as if the windows have been painted while closed, could you get a Stanley knife and slice into the paint.
Another thing to get the key out ....... You can get a small kit for drilling into screws/bolts and extracting them. All you'd need for a replacement then would be something with the same thread.