There still a few out there. But you will be very lucky to find an original perfect W350. There getting old and all are needing some sort of repair or update. Even if you find one that's been tucked away, its going to need a bunch of work to get it going. Just to keep your feet on the ground.
Keep looking setup a few different searches and watch them daily. Have your funds ready.
The last truck I just bought, I looked for a couple months. I found it in the morning and brought it home that nite. A very long day, really the next morning . When we pulled back into the drive, I tow it back from south Florida, because of a transfer case issue. It turned out to be nothing. Better safe than sorry.