I've been reading a bit about the D-Star Dongle, I'm also considering adding the UT-121 board to my IC-91A, I would like to find a place to purchase the Dongle. Not sure where to look yet...so...I'll ask the experts! Oh...new station here so I've got a million questions!
In the U.S. you can buy a DV Dongle at most of the large amateur radio stores. There is also the DVAP which includes a very low power VHF tranceiver.
You can also roll your own.