I was just planning on doing the rings on my Datsun A12 before putting it back in the car but after I opened it up, it needs a bit more work and parts. So far, I've been able to buy "tune-up" parts such as ignition components, gaskets, etc. but I'm coming up short on internal components such as oversized pistons and a cam shaft. Any direction as to where I can get these parts (new) would be greatly appreciated!

Bprojects sells all that stuff via their web site

If you have your old camshaft then find your most local camshaft grinding place and send it to them to regrind for you.

For oversized pistons, identify which ones you want and try your local motor factors shop.

I used Mazda UC 77mm pistons and they were on the shelf at my local shop. I sent my Camshaft to Camtech in Australia.

You can use common A14 pistons in your A12, I see them on eBay regularly. Cheap and they are 3mm oversize compared to A12. The pin size is bigger, so the A12 rods need to be bored out to 19mm

They are dished, so if you want flat-tops you can buy custom ($100 to $125 each) from Venolia, Ross, PAECO, etc.

PJZ usually has some pistons for sale: http://peterzekert.com