where to find belts for Fisher cr-w870 cassette dect?

I have an old Fisher stereo rack ststem and the cassette deck belts have turned to mush. Is there somewhere I can obtain a "belt kit" to replace the old belts. The system itself is a matched ststem and everything else works fine. If there is no "kit" available, are these standard type belts? I could remove the old belts, but am afraid that as stretched out as they are, they would be difficult to "match" Can you provide direction? Thanks