Need key for Yale Mortise lock!

[acwhite]

On Friday my husband and I just purchased and moved into a home built in 1920 and there is a Yale mortise lock on the bedroom door and I have now managed to lock myself out of our bedroom.. There is no key and no way to enter from the window. I see many yale mortise locks on ebay with the keys that go to them. I am wanting to know how many different key variations there were back when this lock was made and what is the likelihood that I could find one online to work in my lock without having to find a locksmith that specializes in antique locks to make us a new key? We had to sleep on an air mattress last night in the living room, I really don't want to have to drill out the lock. Any help would be very appreciated!