I believe that you can use any `79-later CT70 bar and that's about it, as far as anything that looks & fits like the original. OTOH, mount spacing of the later top trees is more or less standardized...giving you a lot of choices among aftermarket bars. Biggest challenge will be finding bars that are as tall.
FWIW, K1-`78 top trees & bar clamps are bolt-on interchangeable with your `79 fork. And the foldable bars can be had as new parts.