In a small PCB I am designing, I wanted a few 3D models that aren't part of DipTrace's default installation. After some search I found this site:
http://www.tracepartsonline.net/They have tens of thousands of 3D models, free to download in several formats, including VRML (which is used by DipTrace). All the models are indexed by manufacturer, type and a few other specifications.
Registration using e-mail is required, but they accepted a "mailinator" disposable mail account.
Disclaimer: I have no affiliation with the site above, and I just found it so helpful that I thought I'd share it with you.