I agree with Kurt, the best (easiest) option is to try to find a complete Athena rear mech cheap on flea bay or similar. Mine only cost me £4 plus postage! If you need just the spring, try Nigel Scott at Campyoldy, if it's not listed he may still have it in stock. If not, then bending springs and drilling holes sounds feasible but far more fiddly. http://www.campyoldy.co.uk