Try to source firing pins, extractor and to a lesser degree an ejector for the gun. Better yet, find an FBP Portuguese SMG bolt group as a drop-in, (I purchased and entire parts kit years ago for $60. Once people realized that many of the parts are interchangeable with the MP40, prices went up). Here is a current offering, which is still a good price, considering what original spare parts are going for:
http://www.ima-usa.com/fbp-9mm-parts...ttachment.html
Norwegian post-war magazines are cheaper than the originals, although hard to find these days. Expect to pay $100+ for original MP40 magazines.
As to accuracy, I can hit clay pigeons placed on the berm 100 yards away 8 out of ten shots, using single shot through trigger control. 30 out of 30 bowling pins is no effort at 75 yards.
Good luck with the most fun and historically significant open bolt SMG out there!