Anyone know of a replacement garbage disposal that is
impervious to dishwasher chlorine?

Check Consumer Reports for their definitive article on disposers. Some of them
have stainless steel internals and IIRC the ratings mention this. As usual, you
get what you pay for and the SS models are the pricier ones.
Stainless is not totally impervious to chlorine, so you may want to review your
current washing compounds and get something less destructive to the
environment. Good luck.

Joe