My system is model no. rt2870r and I have lost the fm antenna wire. Whee can I go to oreder another?

Make of unit?

Is this the "T" shaped dipole antenna using twin-lead?

Are there any balun's involved. Is the input on the stereo just screw terminals or coax?

This? Dipole FM Antenna - RadioShack.com

Other choices: amplified indoor FM antenna - Google Search

I don't know if this RCA receiver is the same as some I've seen, but the FM antenna is often just a single length of wire with a 1-pin connector that mates with the centre pin of a PAL socket on the set.

If this is how yours was, just cut a suitable length of wire (a metre is usually enough), strip about 1cm of insulation from one end and poke it's bared end into the PAL centre pin. You may need to double over the bared copper end to make it a tighter fit in the socket. This usually works fine.

Daniel