www.mpcstuff.com
They sell it for $250.
I don't think it's really that necessary unless you have the interface to run it thru. And even then i still wouldn't drop $250 for it. I'd rater buy some room treatment or some outboard gear or something. I would only get it to utilize the 8 outs.
It's very possible and more common to use the 1/4 " ins to sample.
For a cd player, run 1/4 " cables from the record in to the headphone jack. The same thing can be done thru your pc. You would have to have a cable adapter to combine two 1/4" cables into a single 1/4" or 1/8" plug. Like this one:
Or a cable like this:
. You might also need an adapter to make the 1/4" an 1/8".
For sampling records you would have to run a turntable thru a mixer with a ground terminal then out the mixer to your mpc record in.
With the right cables and adapters you can plug anything ,into your mpc, with a headphone out or an rca out in the back. TV, radio, dvd player, pc, ipod, xbox360, wii, ps3.
Hope this was some help
What's your setup like?