Late reply...
A lot of XRD uses Spectrosil qtz glass tubes to put their samples in. If you have a friendly XRD tech they might be happy to smash one for you. I obtained a few tubes and analysed fragments from each one for Ti (+Al and REE) via LA-ICP-MS. The resulting average Ti concs. from each tube were well within error of each other (~4ppm). So although it sounds like my glass is a little less pure than some others Spectrosil, it doesn't really matter what it is as long as its well characterised.
At the microprobe workshop Karsten just ran here in Adelaide, I gave Dave Adam's a small chip of synthetic TiO2. This material was given to me on request to our local museum (and apparently was quite expensive for them to obtain), but I would be willing to send you a small chip. However....there was no information on its trace composition, AND I haven't had a chance to analyse it myself. So it could be poor material, I just don't know. If you are willing to take that chance I could send you some.
Cheers