There's not really an easier way, exactly, but there is a faster way.

If you collect 99 "Hamstar," every enemy on the Fourth floor of the Seraphic Gate will be Hamsters. Some people call it a "glitch" but I think it's actually intentional for this very reason.

Anyways, if you let them have an "Enemy Advantage" it seems to increase the chance that you'll run into Hammy. It won't be a 100% chance, but it's pretty decent.

And, for anyone who needs it:

Golden Egg: Burgundy Flask (2), Royal Jelly (1), Seafood(3), and Sunflower Seed (1).