I got the one-ball done but I would like to swap out the Cat for a straight-pipe.

where can I get the pipe?

You could probably just have a muffler shop make you one, it would just be a pipe with two flanges on it.

I would like to have it aftermarket so that I can swap it out when the time (smog check) comes. and I also don't like like having CEL on all the time you know?

Just FYI most muffler shops will not touch cats especially ones that are in smog districts. I live in Harris county I have tried to have legitimate work done before and due to the restrictions and fines every last shop I went to refused... I ended up doing the replacement myself.

buy a megan racing header

On a few of my GTi's, my cats collapsed, chunked up causing them to block exhaust pipe and stall the cars.

So I put them up on a lift, I made 3 cuts in the bottom of cat with torch, peeled it back like a door ( wear proper mask and gear !) And hollowed it out, and welded it back to gether again.

Never had any codes come up on dash and they ran great.

i got the cat in my vw gti removed for a straight pipe. I was going to in my MINI but i looked at it , and its fricken tiny! so i said naw not even worth the time. but that would sound great! good luck.