The magnitude data for satellite element (.TLE) files is described at

http://www.fc.net/~mikem/molcdesc.html

This is the "Ted Molczan" format. The same site provides several element
sets that include this magnitude data.

In cases where there is no magnitude data given in the .TLE file,
Guide can often get the mag data from MOLCZAN.BIN, which is essentially
a compressed table of magnitude parameters. Unfortunately, that doesn't
help for new launches...

Some element sets don't even have the name of the satellite, giving
only its designation numbers. Ideally, Guide would have a table giving
a name for each designation number... and maybe some classification
such as "communications satellite" and "US launched", so you could filter
out given classes of satellites.

However, these are all things that I can do by revising the software
after Guide 8 is shipped.

-- Bill