Most of the reproduction parts vendors (look in the Links section) sell the
carburetor insulator. Rebuild kits are available from most local auto parts stores and from many on-line vendors.
Just about any 1954-1962 Rochester carburetor (manual or automatic chokes) should work with your engine (the 235 carb is a little different from the 261 carb - maybe someone else will comment on interchangeability).