So, I managed to strip the drive side crank arm where the pedal screws in on my 1981 Miyata 710. Any ideas on how to fix and or where to find a replacement?

Take it to a bike shop and have them shoot a helicoil into the arm.

If you are referring to the threaded part that allows you to use a crank extraction tool, I did the same thing to the left crank arm (too impatient and stupid to check for the washer).

I managed to disassemble the entire bottom bracket and ended up replacing that and buying a new/used Shimano 600 crankset to replace the damaged crank arm. Right now, the latter is still stuck to the BB spindle in a box of spare parts...

svgeek,
I believe he is referring to where the pedal attaches to the crank, not where the crank attaches to the bottom bracket.

+1.

Oh... In that case, +1 for the helicoil.