There are some shortcuts to dutch angles, especially if you only need one or two occasionally.
One is to turn the camera on a horizontal plane on the tripod head or plate. Now, the head no longer tilts, but it does roll.
Another is to mount a second tripod head on the first, and use the second head's tilt as a roll.
The advantage of the two above techniques is that you can use real video heads, and get a smooth move.
Another is to use a 3-axis still head. The three axis are typically pan, tilt, roll. Hard to do a move, but fine for a static shot.
But, I do agree with luckless about using machine shops for rigs that you can't find commercially, or can't find in quite the right config or cost. Come to think of it, I had a 3x3" tilt plate made a few years ago. All the commercially available were 4x4" or larger. I guess I could use that for a static dutch angle shot, above or below the head.
In areas with a lot of video, there tend to be specialty machinists too, it's a matter of networking through the rental houses to find them.


