I have tried desperately to find super-wide (305x15x60s) tires and they no longer make them!
About the only two tires which fill the bill are Goodyear (etc.) racing tires. These are bias-ply and according to some, not a smooth ride(?!). The other alternative are Mickey Thompsons---again, non-radial and not a known factor (at least by me anyway) when driving on tight and twisty roads.
I really do not want to go with 17" wheels and low profile tires--just a personal preference. Some recent (and some old) posts---the latter being less encouraging---have raised hopes that there may be some 305s coming out in the near future. We'll see!