Hi Mike,
The RealSky disks can be purchased through ASP (Astronomical Society
of the Pacific). You can order on-line through
https://www.mailordercentral.com/aspsky/
I couldn't find a way to link directly to the page in question; you
have to click on "Search", then enter "RealSky". You then get a blurb
giving some details as to what RealSky is and can "click here to add to
your shopping cart".
You can order RealSky North (covers down to dec -16 or so) separately
from RS South (covers up to the equator or so), or order both at once
for $250.
Alternatively/in addition, note that you can download chunks of DSS
(the higher-quality "big brother" of RealSky) through Guide:
http://www.projectpluto.com/update7c.htm#web_dss
This can be a little slower, since you have to download the data
instead of just getting it off the CD. But you don't have to fool around
with CDs; with small areas (a few arcminutes on a side), you spend a lot
of time extracting the Guide CD, swapping in RealSky CD #X, then putting
the Guide disk back in. Add in the higher quality of DSS, and the
download route starts to look pretty good.
-- Bill