Comics Kingdom updates daily and has a comment system, but the archives only span a month. Still, you can view high-res versions.
RBMA Mall sells Slylock Fox collections. I haven’t had the chance to purchase any for myself, but over 40 puzzles for $4 sounds pretty good to me.
Slylockfox.com had an entire section of Slylock puzzles. Thanks to Archive.org, most of them are still visible.
The Slylock Fox Facebook page has a good 280 pictures– most of them puzzles. You don’t even need an account, and most of them are pretty good sized.