Both Shure and Audio-Technica manufacture these "in-line" pads that are basically built into a impedance transformer-type tube. The AT offers 3 settings (-10,-20,-30dB). I have bought mine from BSW, and a broadcast supplier like that is probably your best bet. MI-type stores are not likely to carry something like that.

I'm looking at 6 of them in stock right now...the Audio Technica one with the 10-20-30.

There ya go! Those little puppies are indispensable around the studio and the ATs are great because of the multiple values...

just one more opinion....

The Shure inline pads offer three different levels of attenuation. They are the most transparent that I've heard.