You might want to ask about the card size maximum for SD booting over at gottabemobile.com's Toshiba forum, most of the former M200 owners who would know are there.
I could still find 512MB cards locally at the drug stores with photo printing kiosks or Walmart. I'm suprised camera shops in your area don't.
100% Old School tablet setup:
Sahara i440D - 4GB/500GB/7200 - Vista screams!
HP TC1100 1.2 - 2GB/160GB/5400 - Vista - portrait - primary computer.
HP TC1100 1.2 - 2GB/160GB/5400 - Vista - primary work computer.
HP TC1100 1.0 - 2GB/60GB/7200 - XP - laptop - partner's primary computer.
Acer 303xmi 1.6 - 2GB/100GB/7200 - Vista - laptop - work computer.
Motion M1300 1.0 - 2GB/60GB/7200 - Vista - semi-retired (needs repair).
Motion M1300 - for parts.
Motion M1400VA - awaiting resurrection.