Hi, Grannygamer. Welcome to ebooks and MobileRead!
While Amazon.com does have the largest selection, and you will encounter some titles that only they have, most of the time you can hunt down an ePub version somewhere.
Try searching at
Inkmesh. The results will say what format the ebook is in.
It's just a matter of time before ePub selection rivals Amazon's Kindle store. It's already nearly there, just not all in one place. Amazon worked hard to get a head start but there are only so many books in the world. Others will catch up.