Do you want a real card (something that plugs into the motherboard bus?
Or a USB interface? Or would you be happy using your computer's built-in
audio hardware if you could plug things together?
Thing is that the type of connector is arbitrary. You can adapt anything
to anything, though sometimes it takes a little knowledge. If you just
want something inexpensive that mates up, the Behringer UCA-202 works
quite well. Its only problem is that it's designed to work at a
moderately low signal level (like the Tape Output of a home stereo
receiver) any depending on the mixer and how it's being operated, what
comes out of the RCA jacks might overload the inputs to the UCA-202.
You'd need in-line attenuators in addition to an RCA cable, and there
you go with another "adapter."