I do struggle finding a 12V powersupply unit ...
When you say power supply unit are you talking plug-in ones or an external battery?
Plug in 12v plug in wall-warts are to be had for about £5 or $8 from eBay (just be sure they won't burn your house down, some of those Far Eastern units can be a bit dodgy - sometimes better to pay more).
12v batteries are of course readily available - a small rechargeable li-ion or even a 'wet' gel-type motorcycle battery are generally available.
Perhaps you can detail your exact requirements more fully for better answers.