S3C catalytic pipes

[JapS]

Hi everyone.
S3C engine revs better by rechecking distributor timing.
However, the power feel is not good.
Catalytic pipes melted and I had to get rid of melted catalyzer.
So exhaust pressure is lower than normal,especially at low rpm.
Removed catalyzer coused such a low power feel or unstable idle?

And for automotive inspection like a MOT,I need new catalytic pipes.
How can I get new pipes?

Thanks a lot