I have not been able to find an extensive collection of RPGs since the Trove shut down. I know there is a torrent backup somewhere but i do not want to mess with that currently. The Eye has some stuff, but it is very limited and the usual Ebook sites also only have a small and very random selection.
Pdfcoffee, scribd downloaders, anyflip kinda.
I mostly use torrents or get them directly from other people, most direct download sites i know about are kinda scuffed.