Dear "Poor Aussie":
Since you need SOI with a thick layer (15 micron) of silicon film, you may only
have the option of Bonded- and-Etchback SOI (BESOI) which permits such thicker
layers. The alternative is (oxygen-implanted) SIMOX wafers that subsequently
require epi-silicon grown on a thin 200-nm silicon film.
For BESOI, you might try contacting either SiBond L.L.C. (Hopewell Junction,
NY) or Shin-Etsu Handotai - SEH (Isobe, Japan or Washington State, USA).
----R.W. Griffith