I am having 405nm AR coated single element glass lenses made at the moment, and they will fit wherever an AixiZ lens nut fits. They are designed to have a FL between the acrylic and the Meredith lens. Glass will let more 405nm light through and the slightly longer FL will allow for easier focusing than with a Meredith. In the end, they came out very similar to the Meredith glass lens, only slightly larger.
I will be testing them in just over two weeks, and if they work, i could order a larger quantity. I am paying a fortune for the first batch, but a group buy could bring the price down, if enough people were interested... The tools will already be made, so it would also go faster. The slowest part would probably be the GB itself.
I also ordered some of them with a Multilayer coating. Costs 1 Euro more, but they would work great with reds (or any other wavelength) as well.