I got mine from All Electronics. But there's a problem! The battery goes dead quickly, and is non-replaceable!
Step 2: Uncovering
Take off the back cover, and locate the battery connections at the bottom (here left) of the unit.
Step 3: Soldering
Solder the single AA battery holder as seen here: red to + on the PTT side, black to - (GND) on the other side. It's also quite simple at this point to take the soldering iron and melt a small channel in the side opposite the PTT for the battery wires to come out of.
Step 4: Connecting
Now connect the coiled wire to your HT, put in a AA battery, and connect the two audio cables to your PC: the Mic on your PC goes directly into the speaker jack, and the Headphone on your PC goes through a 3.5 mm to 2.5 mm adapter to the mic jack on the VOX unit. You may have to tweak the volume and vox levels, but mine worked right from plugging it in. Boot up AGWPE, start up UI-View, and you're good to go!