At the moment, there aren't all that many turbo E46s out there. This is the only one I could find.
http://www.atpturbo.com/root/monstermate/bmw3ser.htm
I honestly dont know enough about it to suggest it, but it seems to be one of the few turbo options out there. I wouldn't be suprised if Dinan or one of the other major BMW tuners came out with a Turbo package soon. So yes, there is turbochargers for the E46 M3, but it isnt that common.
Good luck with the test drives. Let me know how they go. Make sure you test both a manual and a SMG M3.