notfourchan seems to be the one that generates the most new material. Particularly their /t/ board. 7chan /l/ is rife with newfaggotry, but occasionally you'll get some people in there that deliver in a big way.
12chan has an /l/, but I never go there. I assume it's slow as fuck, like the rest of the board. desuchan has an /l/, but I think it's pretty slow too.
Best way to find new stuff is to start keeping track of artists and scour TT for known loli releases, like LO, RIN, and artist compilations.