Yeah, I've got a weird old SR with a similar BCD problem. Luckily I picked up another bike that just happened to have the same, strange BCD, but if I burn through these, I'm outta luck.

I don't think you'll have any luck replacing the outer ring, but who cares? Like you mentioned, the crank kinda acts like a chain/bash guard, so you can just run on the inner bolts and you're good. That's how my conversion is setup, and me likey. If you're a pack rat / insistent recycler like me, keep the ring in your parts bin. Actually, you should just keep it around for the "check this thing out" value, even if you never use it again. I mean, c'mon, 190??