I recently bought a used chronarch ci4 that is in desperate need of some new knobs. Are the shimano handles compatible with any other brands of knobs at all? Is there any other shimano handles that are longer that can be swapped on?

You probably won't be able to put any Non-Shimano knobs on a stock Shimano handle. An after market handle, would but that would depend upon the handle.

As far as a longer handle I would like at the Met XG handle assembly. Much cheaper than buying a carbon fiber version if you aren't willing to shell out a lot of money for a handle.

The only other knows I can think of that would fit would be yumeya knobs. Most I've seen are the skinny little metal knobs, but they do make round cork knobs also. Hawgtech, semper fi, avail, yumeya, and livre all make handles that fit shimano, and some may have knobs that fit. Hawgtech makes cork knobs that fit their handles and shimano stock handles. The cheapest way out is to buy stock knobs or metanium xg 96mm handle that kickerfish mentioned. It's plenty long enough imo.