I have had a few Biggs engines apart. First thing I would do is go to Briggs and Stratton's website (
https://shop.briggsandstratton.com/us/en ) for parts. I have found out the best thing for engine parts and engine info is go to the manufacture that made the engine. I would purchase parts from a local small engine dealer.
Another site that may be able to help is I Save Tractors (
http://isavetractors.com/)
Briggs used to have rebuild kits. Not sure what Briggs has now for the old engines.