I've built a couple of spectroscopes using 1200 lpm gratings based on an old BAA design and now want to uprade to a Littrow design based around a 200mm photographic lens, similar to the WPO design of Maurice Gavin. This design really needs a 40 x 40mm reflecting 1200 lpm grating.
See
http://www.astroman.fsnet.co.uk/newspec.htm
and
http://users.erols.com/njastro/faas/