There are 3D models of each of the main 6. We just need someone with a 3D printer to print them out.
While there are models of the mane six, I don't consider them "worthy" of printing, some of the designs don't have high enough poly count, or their proportions are awkward, that Pinkamena was designed to be printed from CAD, but there are very few people who can use CAD for that sort of thing (Well Bronies and that I know of, an artist could, but I'm yet to see the first person who models figurines on AutoCAD).
However the main problem is copyrights, after all, you are reproducing a figurine from a toy which is a figurine, that is the main problem that I see with the printing.
As for 3D designs, none of them (expect that Pinkamena and the Lyra design in 3DMax on ponychan) have enough quality to deserve printing, and I'm pretty sure that there are artists who can model those ponies from porcelain or some other malleable material and can kind of
skip or
overlook that copyright infrigement.
(And yeah I'm aware that it gets into the whole MLP branded stuff that shouldn't be done, but figurines are the closest thing that I can see as a toy that might get Hasbro crossed).