Hi, everyone.
Believe it or not, a nice way to get crafting runes is Disenchanting.
Disenchanting low level items (14-20) yielded more Blends, Disenchants and Activates than just killing things at-level. Mind you, they are randomly distributed so you wont get stacks but you will get something useful that is worth the time you spent doing it.
Levels 14-20 seems to yield mostly Blend and Disenchants. Around levels 25 seems to be Frost Runes more than the latter. The little area before Ravenfell, outside Varanas, has a lot of guys that always drop green and white stuff no matter how high you are if you have a housekeeper potion. After 10 minutes, I had almost 10 of each of those three runes.
I have no idea if the rune-finding certificate has anything to do with Disenchanting results.