I went to the junk dealer in bugtown and didn't see anything for 8k (As I had read in other posts), or any clickable boxes in his tent as was suggested.
I'm guessing the guides on Matrix Cubes are a little out of date as you also can't put on in your ship hold anymore- how can I disassemble my cube?
-Azerin on Hanharr
The Bug Town junk dealer sells the key to the lockbox that in the tent next door. Inside that is the disassembler. It has the word Tatooine in the description and refers to a shipment. Are you sure you went to the right vendor? He's all the way across the lake from the arrival platform. He also sells the key to unlock the lockbox that houses the datacron. I was just there last week so the datacron guide info is correct.
The Tatooine Jawa junk dealer is easier to get to (if you are Imperial). He's located in the junk yard on the north end of Mos Isla.