Depends how realistic you require. If you want realism, get the taxidermy style. If you want round pupil or maybe cat eye, you can sometimes find them at places like Michael's art stores, or places that sell doll making material.
Yes, doll making material. Get ready for some strange looks if you find a specialty type store. The doll type eyes often have a "post" that extends behind the pupil that you would use to push into the doll eye sockets.
When adapting one of those to baits, you can cut off the post or snip it off with clippers if it hinders your design.
Also, with glass eyes, weight is a major consideration since they are way heavier than the type BobP mentioned. For that reason, eye placement is absolutely critical when using glass.
Good luck.