gn_n_60_shelby started a thread earlier this year looking for the supplier of CR II side pipes. If he's had success in that regard he may have the answer, otherwise this topic has been covered repeatedly and you may want to check out these threads:
Classic Roadster exhaust dilemma
I re-did my car's side pipes... AGAIN.
As others have noted, in this thread as well as the links above, the original side pipes are quite restrictive. Replacing the mufflers with other, higher flowing, mufflers will uncork the exhaust and probably the cheapest power adder for your CR II.
If your pipes are chromed or plated you'll have some additional challenges, but this could be your justification to have them ceramic coated!