I have been using srsLTE for about 5 years now, and about 3 years ago physical USIM support was added to it.
Did you really mean srsLTE as in network side, or did you mean srsUE for LTE UE side? The latter seems to make a lot more sense for USIM support.
srsLTE is the global project ( https://github.com/srslte/srslte ) and it encompasses srsENB / srsEPC for the network side, srsUE for the mobile side along with a bunch of utility internal libraries shared between those components.
Rgds,
Sylvain