Where should I be Buying Omnibus’ from?

I’m fairly new to collecting Omni’s and I try my best to support my local comic book shop, however they don’t have a huge Omni selection and those they do I can find for half the price elsewhere (I still bite the bullet and support them though most the time). I have started just pre ordering new Omni releases through them for example the ultimate fantastic four coming out next week I’ll be getting from them.

However for books already in print I’ve been looking around for new places to purchase from and want to know where yall have had the best luck.

I read everything I buy and I have no problem with some dinks and scratches here and there from second hand purchases.

I’ve looking into r/comicswap but am very intimidated and don’t want to break their rules.