The only TLR that I've heard of that has interchangable lenses are the YASHICA and they(lenses) are pretty rare and fairly expensive. Depending on your lense mount type you might be able to find a close up X2 or x3 filter lense for macro work... Rollei TLR have a wide angle attachment built specifically for them but they are INSANELY EXPENSIVE!!!
The Mamiya C330 uses interchangeable lens but they are expensive.
I think for the Sea Gull and the Yashica you should be looking for AUXILLARY lenses. Yashica made an auxillary wide angle and auxillary telephoto lens. I don't know if the mount (3 prong bayonet) will fit the Sea Gull.