As I understand it, Gregg ruled paper is three lines to the inch.
If you can't get hold of proper steno pads (like here in Germany, where Gregg never really took hold!), one way out is to print your own.
http://www.incompetech.com/graphpaper/writing.html has several different PDF generators.
The lined paper generator may be useful (it lets you specify the line spacing in lines per inch), or the notebook paper generator which gives you a line down the left-hand side; the "wide" spacing is pretty nearly three lines per inch, as far as I can tell.
If you want a line down the middle and three-inch columns you can also give the simple asymmetric graph paper generator a try: set the horizontal spacing to 3 inches, bold every 0 lines, and vertical to 0.333 inches, bold every 0 lines. Or if you want wider columns on 8½×11" paper, try 3.7 inches for horizontal spacing.
(by Philip for everyone)