Touch screen drivers must have existed in some form at some time for the Newspad. If we are very lucky Castle may have the module on a disk somewhere.
As my missing reply went on to say... I am also thining if the device goes out of production as long as you make sure you pick a device that was sold in sufficient numbers to ensure we continue to have a strong 2nd hand market and parts/accessories are available for a number of years. This would mean you could switch from selling the devices pre-installed with risc os to selling ROM upgrades (either a replacement plug-in rom board or a flash upgrade service).
By following the above route it would mean they can still continue to sell the service/product and continue to make money from the investment made to make the OS work on the device in the first place even if the device is no longer available new.