I haven't seen any consumables other than Noth's, but with a Plague Strike and Icy Touch I've got enough to kick-start me, then I use Death & Decay which boosts Rune Power a bit more, as well as having its AoE. There's always Empower Rune Weapon, for 25 Runic Power, as well, albeit with a 5 min cooldown.
Anyway, from zero Runic Power to around 30% takes a few seconds, then after that I have so much Runic Power I don't know what to do with it!