A very short video here guys. I spent quite a while trying to locate this specific roaming vendor, Dave Oshry, so that I can get myself allot of good gear.
As described in the video if you go and look for him make sure you do the random encounters. I'm not sure but it feels as though the game has a hidden setting that every 4th to 5th encounter will be a roaming vendor.
This guy is definitely worth killing for the amount of loot you can get from him.