I bought them on eBay. You can buy a suitable power supply for a lot less than $8.
Here you go, eBay: 251998381314, 25 of them for $2.47 free shipping.
For $4.68 you can have the power supply with the proper barrel connector, eBay: 371165009256
I just received the power supply from China on July 15, 2016. It appears the unit will power a TIU, however; it requires a special power cord for the 110V power. The end of the power supply has two round male barrels, that would receive two female portions to slide over them. The power supply has a special receptacle that has two round cutouts to allow the cord to plug into the power supply. Each hole is abut the diameter of a pencil. Any ideas where I might find such a power cord as without it there can't be a source of power from the 110V? I can't see using alligator clips as I'm not sure about polarity.