First, need to know yer city/state...so we can point you to a good gunsmith
in yer area. TXfeller is right, a good gunsmith should be able to take the busted one & make a new one.
Second, on the cross-reference chart there isn't a model 5540...hope that's the serial number

Might need to disassemble it and check EVERYWHERE for numbers...hopefully you'll find a set that helps
Third, if you can, take a few pics of it and upload it to the gallery here...then put a link up here to it

Might be that we can recognize it from a few good pics if we can't get a Model #