Have you tried RepRapLtd? Even if they can't supply the PTFE tube they should at least be able to tell you the correct dimensions.
Ive looked in their shop, but they do not sell ptfe tube that goes inside the nozzle, only the bowden one.
Since I need to print asap, I just ordered a new 0.5 nozzle that comes with the ptfe tube in it.
Sorry - I was away last week so didn't catch this post until now. We've got bags of the stuff - It's listed here for future ref: [reprapltd.com]
Always worth sending us a message if you can't find what you need as we have a lot of components that aren't necessarily on the webshop or we know where to source them.