Astrophotography: Best focusing screen for Pentax MX?

Hi,

I have a Pentax MX that I have used a few times for astrophotography,

and am trying to figure out the best way to brighten up the

viewfinder. I read on Boz's page that the focusing screens from the

LX will also fit the MX, and there was a screen made for the LX

(screen SD-11) for this purpose, but I can't seem to find anyone who

still sells that particular one. Of course there are also the third

party manufacturers, but I've no experience with any of those. If

anyone has any recommendations or info I would appreciate it.