Depending on the final goals and how much 'like' the interface you're trying to get, there are a LOT of mixers that can do what you want. In fact, I actually mapped the channels, crossfader, and quite a bit more to my mixer so I could spin video with turntables.
What you need is a mixer capable of sending audio and/or MIDI on each control. Some mixers are clearly one or the other (Behringer DDM4000) for example, and some mixers can do both (Pioneer DJM800 I believe does this).
The limitation of the DDM4000 is if you use everything for MIDI then the audio comes through at full volume. Since I was only using two decks at a time, it wasn't that big an issue - I used channel 1 for the 'live' audio and channel 4 for the PFL, and then 2/3 was setup as MIDI control for the two decks in use.
If you were going to use the mixer as JUST a MIDI controller you could do that too - but then the output off the soundcard would go straight to the PA or would have to feed another mixer.
In the end, it comes down to how much MIDI control do you want on the mixer and how much audio control?
Another possibility is to pick up a Behringer CMD MM-1 which is a 4 channel mixer layout but is MIDI only. MAP is about $129 or so.
http://www.behringer.com/EN/Products/CMD-MM-1.aspx It's half the size of a standard record.
You can add on other controllers as needed to control anything you wanted. FYI - Since these are new they aren't mapped yet, but I'd expect them to be mapped by the public at least pretty quickly. They ship with Traktor, Serato, and Deckadance mappings.
might want to look at the 4 player mixers also ,, 
