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The two big distributors I use are Allied Electronics and Newark Electronics -- both carry Analog Devices. Future Active is also very good, but sometimes you need to purchase a lot of 500!
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).