There's a significant difference between the ELDI/Union system (they're the same, or used to be), and a helicoil type insert. The solid bushing design calls for more hole enlargement than a spring which only requires the thread height (1/2 height per side).

There's little, and based on plenty of experience in use, no material loss of crank arm strength. I suspect a co-op would have one or the another system since they deal with this kind of stuff every day. Also, any decent shop should have one if they do repairs to any significant degree. I sold many dozens of these kits when I was a wholesaler, and I believe QBP still has them for sale.

FWIW - the right side is a stock item since it was a popular spark plug thread. BITD - the maker was willing to wind LH coils for me, but only if I committed to 100 taps, which I did. It might be that if nobody will commit to the LH taps, that version may no longer be made.

If there's no co-op near you, look for an older shop who's mechanics actually fix, rather than simply replace parts. There's no logical need for an individual to buy the tools because it would never pay for itself.