I've seen rebuild kits from time to time on eBay, you may be rewarded if you are patient. Or you may find an eBay donor ratchet.
It's just the lever that's the problem? If you just want it to work, I would think a little patience and you could craft something to do the job. A couple of holes drilled in a small piece of stock, filed out, epoxied or peened in place... painful to do, and honestly probably a better value to buy another ratchet like it and save your time, but possible. Or try swiping and modifying a part from another with a similar lever design - seems to me some older Proto or Armstrongs had a lever like that, and there are China knockoffs around that the lever from them could be made to work.
I do appreciate keeping these things going, and Indestro is cool (I particularly like my 1/4" round-head Indestro Super ratchet). Worst case is leave a message up here, this is about as likely of a place to find parts for it as anywhere.