Mike Ellek's webpage has instructions and illustrations for making a take-up spool out of a 35mm cassette spool for a Kiev. The gripping mechanism for the Fed-2 is different from that of the Zeiss design Kiev.
It's not impossible to make your own Fed-2 spool, but a replacement should cost you no more than $10 (US). You may also be able to get a whole bunch of spare parts with it (most of a camera).
From what I have read, Fed's are a lot more common at "boot sales" and camera stores in the UK than they are in the US.