hrst, I would definitely love to get my hands on such a gizmo. Looking at your past electronics skills, I have no doubt you can make one! Nevermind my previous neigh-saying...
Ok, so attached is a depiction of a typical step wedge like we all use (Stouffer), and then an ideal form for a spectrosensitometer. We need something that's more "squat". Hamburger as opposed to hotdog... if you will. Right?
Now why is a thin slit so important? That spectroscope article suggests that it should be 2-10 mils wide. Why does the light have to be collimated exactly?
I've found 500 lp/mm and 1000 lp/mm diffraction gratings on eBay for very cheap; like the attached image. I think I'm going to just have to buy these and play around with them to see how they act in different circumstances. Again, in every diagram the diffraction grating or the focusing lens is oriented at an angle; is this the only way to get the diffraction grating to "do its stuff"?, that is, to spread out an image of the spectrum.
It'd be ideal to use plastic lenses so that we don't alter our UV transmission much. Cheap acrylic lenses abound, in all different types of powers.