For a scientific project I'd need a linear polariser where I can control the polarisation angle on a pixel by pixel basis.

My idea is to use an LCD, with only one polariser installed. Thus, the light entering the LCD will be polarised in one direction and depending on how much the particular pixel rotates the angle, I can have an image that has a pixel-by-pixel controlled polarisation. Note that I don't need the LCD to change the light intensity, only the polarisation angle. For a human eye the resulting image would not be visible (unless one wears polarising sunglasses).

However, I need the wavelength range to go from 350nm (UV) to about 600nm (green-yellow). That, if at all doable, is obviously a custom job. I know that there are LCDs that work at 405nm, UV-curing 3D printing uses them. But I don't know whether they go down to 350nm and simultaneously up to 600nm. In fact I don't mind if the polarisation is not that great at longer wavelength, the most important range is the UV, but the panel must be at least transparent to visible light as well.

I wonder if anyone knows custom LCD manufacturers who might be able to do something like that? We're talking about pretty low volume (about a hundred panels), so probably companies who specialise to millions of pieces per year wouldn't talk to me; I need to find some niche-market  LCD manufacturers who can cater for seemingly deranged customers...

Any pointers would be appreciated.

I've never done a custom display so I have no idea if what you're proposing can be done or not. I've used a lot of displays from Newhaven Display though with success, and they do custom jobs according to their website.

You might try contacting Adafruit. Not that they would be able to make one, but they might have the right contacts. They might know a guy who knows a guy (or gal!) who could do it.