We posted about Rock Band 2 preparing a way to produce a 3D print of your character, and now it's actually available to the public!
If you head over here, you'll see a section entitled, "Make Bandmates", where you can "Order custom-made, detailed 6 inch figures of your characters!"
However, commenter Lawman points out that:
This feature applies to the PS3 and Xbox 360 versions of the game ONLY, since they have perpetual network sign-ins and let you edit your own characters. Conversely, custom figurines don't really apply to PS2 or Wii, unfortunately.
He adds that other services like Figureprints can perform similar services.