Is there a product available that is pre-gelatinized starch and what product name is it sold with? I am trying to make packets of instant pudding that do not need heating, in order to thicken the mix to form a cold dessert. Some sanity has to be found in my kitchen, as most foods are home cooked because of my allergies.

I have attempted to test rice paper and tapioca flour (Australian brand and Chinese or East Asian product), potato starch, and puffed amaranth breakfast cereal, thinking that some value or gel might result from my efforts.  (It has not.)

Inquiries regarding pre-gelatinised products result in blunt dismissal, as those products here in Australia are reserved exclusively for medical reasons to celiacs or patients with problems swallowing, and supply is restricted to local chemists.

Is the supply of these products restricted by requirements for a doctor's prescription? If not, how or where can I obtain them?
Yeah, what you want is UltraTex-3 (or possibly the 8 or UltraSperse variants), from National Starch. Willpowder carries them: http://www.willpowder.net/tapioca.html

You can make something very much like instant pudding from just about any liquid using this stuff, and it can be cold. No heating required. Works best with a stick blender.