A few years back I designed a series of silver Tardis rings for my shop: Sleek and Destroy. Coincidentally you might also be interested in the Lock Pick Earrings I designed as well.
I don't have any plans on restarting the series, and it seems right to release the design to the community to use, remix, and play with. I've uploaded the SolidWorks file for direct hacking, along with STL's of the ring in several common sizes.
You can find more info and photos of some completed silver Tardis rings here.