Try calling these guys:
https://egge.com/. I just rebuilt the entire low end and they had everything except mains.
For main bearings, intake valves, and cam shaft you will have to find NOS on eBay. I found most of the other head rebuild parts on Rockauto. To my knowledge, NOS replacement crankshaft and pistons are non-existent. I think there are places that can build you a set of pistons, but extremely expensive. I would try to resurface the journals on your crankshaft and reuse your pistons and install new rings.
The gasket set is FEL-PRO HS7961SB1 (minus rear main seal, oil pan gasket and timing cover gasket). I got mine on amazon
https://www.amazon.com/Fel-Pro-Hs796...-PRO+HS7961SB1. Rear main seal is FEL-PRO BS 40048. Oil pan gasket is FEL-PRO OS 34404 C. Timing cover gasket is: FEL-PRO TCS 12937.
I recommend finding a spare 305 engine to keep around in case you need parts. I have 2 right now!