Humble Bundle, Indie Gala, Indie Royale, Ect.....

Buying past bundles seems to be near-impossible; you might find some of them randomly, such as here on SteamGifts, or when HIB4 included HIB3 or IG2 included IG1, or through an as-yet unused potential feature where Indie Royale plans to feature old bundles that were really popular (based on IR customers putting bundles they didn't buy their wishlists).

As for bundles, there's Indie Face Kick and Groupees Be Mine and maybe a few others. Check out this site or this site for bundle trackers.

Thanks for the info. Gonna look at the sites you gave me and do a little research.