Had to look that up and found it to be a very old computer, In my quick search I couldn't find the computer itself but I think I found the Popular Electronics Mag you were looking for, here
(Link is too big to paste directly here)
It seems your best bet is to look on Ebay for the computer because that is where I found the Popular Electronics Mag, plus I hope you know the estimated cost that one of those could be ($1500-$3000), one sold here on Ebay
for $3500 2 weeks ago although this seems to be a different one to what you want (Altair 8800b TurnKey, which seems to have been the latest model/version of the computer), quoted from here - http://www.virtualaltair.com/
Hope that helps.