Are you looking for a wah pedal or an expression pedal to control the wah effect in POD Farm?

Are you using the plug-in version or the standalone version of POD Farm?

If you're loooking for a wah pedal, any wah pedal will work. Just plug your guitar into the wah pedal and run the output of your wah into the TonePort or POD Studio.

If you're looking for an expression pedal to control the plug-in version of POD Farm, any MIDI expression pedal should work. POD Farm doesn't support MIDI natively, but just about every DAW lets you map MIDI CC mesages to VST parameters.

For the standalone version of POD Farm, I think you're out of luck. But you could downgrade to GearBox, which has full MIDI support, and then you can use a MIDI expression pedal for this, too.

And if you're patient, I'm guessing Line 6 will add MIDI support to POD Farm sooner or later -- but that's just a guess.