Hi Benjamin
I just analysed the camera lense i can see that the glass is pasted probably with a double sided tape to that white plastic piece as shown in these pics [http://d3nevzfk7ii3be.cloudfront.net/igi/IDhhPQYnCBogaKT3.huge|Pic 1] and [http://d3nevzfk7ii3be.cloudfront.net/igi/IBoDJHhMsrBMOVGZ.huge|Pic 2].
So it should come out without taking the phone apart.
I am not sure we get just the lense as a separate spare part.
Still you can measure the diameter of the glass and probably compare it the diameter of any previous HTC phone or a Sony phones as they both use same kind of round glass as lense cover.
If you think i answered your question please rate (score) and mark it accepted. :)
Thanks