Any universal rack , a *decent* bike shop should already have these little trinkets in stock.

J&b has the seatpost clamps, with the additional built in rack mounts ...
also, there are really long "straps" available.
straps:
http://www.jbimporters.com/web/check...t_number=45853
clamp: ( sized for carbon frame, lol. )
http://www.jbimporters.com/web/check...t_number=51866