... a River Class frigate ...
I think, all big mods have a model of the River Class included. It was one of the early attempts of creating additional ships. Bigboywooly did it. It is basically a transformed stock SH3 Black Swan model, which is consequent since the River class design derived from that of the sloops. In combination with the GWX textures the model looks quite fine.
Kendras, you may try the model of the River Class frigates that came with SH4. Pretty ugly ...
In brief, I never did a model of the River class and I do not think I will ever do.