Can anyone recommend...

[bassthunder100]

A site that will build me a parallel looper with 2 channels and a phase inversion switch?

[Low Sound Love]

try building one yourself, making your own pedals is fun and not too hard, really.
if you search for a bit, i'm sure you'll find a fitting schematic.

I'm making my own fx blender soon, one fx loop with blend knob and phase inverter ...

[N.F.A.]

Try Brad Davis at Creepyfingers effects. He is world class.

[cheapbasslovin]

http://www.badgereffects.com/para.html