Checker Auto Parts (and maybe even Auto Zone)handles the SCHOSHE (sp?) of automatic power antennas.
I have used them on a variety of cars and have had good luck. There are two models, one for about $60.00 and the other for about $80.00. I used the latter one as it had more adapters and a bigger motor unit. Both have long connector wires to the radio unit and both reach over 36".
If you want to wire it so that it won't come up when you play the cassette or CD, just wire in an SPST (on-off) toggle switch. There are only three wires to hook up as I recall.