I bought my rebuild kit ($48.67 plus reasonable shipping) from Columbus Diesel Supply, 1575 Integrity Dr East, Columbus OH 43209, phone 614.445.8391. The kit includes the two bearings plus other parts (see pic; bearings marked).
There are a couple of threads (for example,
http://www.peachparts.com/shopforum/diesel-discussion/17299-turbo-rebuild-post809807.html#post809807) that refer to a place called M&M in Houston, but they couldn't sell me parts because of some regional distribution restrictions (I live in Virginia). You may have better luck depending on where you live.
You'll need to know the part number of your turbo, which you'll find on a little plate on the back side of the compressor housing if yours is a T3 like mine. It should be the six digit number (or six plus one) that starts the second line. Mine, for example, is 465228-3.
Note the Garrett rebuild kit does not include the gasket that fits between the two halves of the compressor housing, which you will definitely need to replace. I ended up buying one from a local guy who rebuilds turbos for a living: Tim's Turbos, 3217 Annandale Rd, Falls Church VA 22042, phone 866.3TURBOS or 703.241.7411. He also cleaned and balanced the shaft assembly for about $50. He has a website (timsturbos.com) and an email address, but I'd recommend a phone call. He may be able to hook you up with everything you need, including a complete rebuild job should you decide not to tackle the job yourself.