A derivative of http://www.thingiverse.com/thing:19468 . My printer didn't print it (the balls didn't stick to the bed and printing with raft was no good either), so I had to change it a bit.
And as I don't have SketchUp, I made a openscad design that had the same dimensions as the original and added some sort of support structure there.
It is usefull either for bragging or to include it as a part in your thing.
Use the stl directly if the dimensions (inner radius 11 mm, outer radius 30 mm, height 10 mm) fit your needs. Otherwise use the scad file and adapt to your needs (rendering to stl takes quite some time on my PC, but yours may be faster).
Slice (I used 0.3 mm layer height, 2 extra shells (in an attempt to avoid the warping of the balls) and no extra support or raft) and print (I used ABS). Then try to clean up the balls as much as possible as long as they are still fixed by the support structure. I first cut the ring like structure and used a needle file to remove the bumps from the balls. The last step is to cut the balls loose from the bearings. (After that it is quite difficult to clean them any further.) Enjoy!