Focusing screen for *ist-DS

[David Oswald]

I haven't seen anyone selling alternative focusing screens for the 
*ist-DS, though screen interchangeability is listed as one of the 
camera's features.  Has anyone seen them listed for sale anywhere, and 
if so at what cost?

What screens are available?  I'm considering picking up an 'A' lens 
(pre-autofocus), but I'm hesitant because I find that the matte focusing 
screen sometimes just doesn't get me 100% of the way there.

In particular, I keep drooling over an SMC-Pentax A 135mm f/2.8.  You 
see FA's for sale occasionally here and there, but 'A's are often less 
expensive, and if I could jsut feel a little more comfortable with my 
ability to achieve decent focus I'd go ahead and get one.

I remember as a kid using my father's Olympus OM-2n, with its 
split-image, surrounded by some sort of prism, surrounded by matte. 
That seemed to be an ideal screen, at least to my young eyes back then.

Dave