Rarity of Runes?

Are some runes supposed to be more rare than others? I am over level 60, and im almost done with Act 3 cruel. But throughout that entire time i only collected 4 iron runes. i used them when i crafted better weapons to carry me through the next few acts. but i havent found anymore since after about lvl 20-30. i just reforged well over 80 of the other kinds of runes and still didnt get any iron runes. Are they that hard to come by? do you get more of them at lower levels. im having difficulty getting decent stats/rolls for the stats, so i figure if i can at least get the runes i can improve my damage guaranteed that way.

sorry for the long post, but all that was to say that iron runes feel really, really, really, REALLY rare. I have gotten more exalts than iron runes to be quite frank. And before anyone mentions it, im playing SSF, so i cant trade for them. and i used up what few exalts i had trying to craft decent gear(to no avail)

In campaign they appear rare, once you get to maps, you'll stop picking them up

I don't think the iron ones are more rare per se, just that you will use them as fast as you can find them.

Probably still very cheap on the currency exchange if you run out.