I am no help; this is one of the biggest reasons I use EQ7, it does all the math for me.
If you aren't familiar, it's Electric Quilt 7, and they now have a sort of "lite" version of it called EQ Stitch; it's computer software and you can choose/create any quilt layout, blocks, etc, and even color it and it will tell you how much fabric is needed for that quilt. So...not specifically "how many triangles per yard of fabric" but will give you how much yardage you need for a given project, if that makes sense.
You could probably get it to do so by creating a One Patch quilt, set to the size of whatever piece of fabric you want to cut (so, for ex, 18" x 22" for a fat quarter) and then make the patches whatever size/shape you're wanting to end up with, and it will fill in. (I guess you'd have to count how many show up...).
Let me play with it a minute and see if I can get it to do what I"m trying to tell you, and if so, I'll come back and post how many 60* triangles of that size for a yard of fabric. Be right back.....