Good luck on your parts search. I agree with the others that fining the "original" parts will be virtually impossible, but I would think that with some (possibly considerable) effort you should be able to find someone with a stash of old H&H lock parts to use as a starting point for the restoration.

70 Pounds doesn't seem all that unreasonable to me. it's $100.00 to get a factory letter on a Colt Single Action, and the only information you get is the original configuration of the gun (bbl. length, caliber, finish), shipping date and shipping destination. If the gun was factory engraved, or has some historic connection the price can go to $300.00 or more.

Best regards,