Where can I buy super-opamps??

Digikey does carry LT

LT -- is for Linear Tech, I believe that Digikey is their exclusive distributor. Digikey also carries Texas Instruments and Maxim, and as you point out, Nat Semi. They are a trifle expensive for Nat Semi parts -- a lot of the stuff I use (for instrumentation) can be more cheaply had at Jameco, but I don't think audio types are big into '353s and 412's.

By the way, Linear Tech's technical support is excellent. (not to diminish ADI, NSM and MXIM who are also helpful).