I’ve updated the 3D printing page to include Chemtube3D which has a number of chemical reaction transition states in both the .stl and .x3d format which work with most printers.

A list of available transition state classes is shown below:

• (C=O) Nucleophilic Substition and Addition
• Pericyclic and Diels-Alder Reactions
• Heterocycles
• Rearrangements
• Radical and Stereospecific Reactions
• Organometallic Reactions