Are you referring to torrent sites that only exist within Tor/I2P/etc. ?
Or are you referring to public torrent sites that also have an Tor/I2P address to access them? There are a fair few torrent sites that can be accessed that way e.g.
Think(?) there are 1-2 torrent indexes within I2P, been years since I looked at those & they weren't all that interesting IMO. You could probably find them if you look around at I2P listings.
Please don't torrent over tor. I2p was designed with p2p and torrenting in mind but the topology and routing scheme used in Tor makes p2p file sharing painfully slow and drags down the performance of the whole network.