I just released 2.0 of
Nature Summoning. This is a big overhaul of the mod. I removed two of the summonings as they felt redundant. Now there are just Wolves, Sabre Cats, Bears, and Spriggans. However, I also added permanent Thrall-versions of each, in addition to the Potent versions you will summon if you have Elemental Potency. I also added spell vendors to the capital of every hold, making it easier then ever to buy the spells. They also have a random chance of having a soul gem for sale, and the Master Trader perk will work with them.
The vendors can be found in the following locations:
Whiterun: Morcant, in the Temple of Kynareth.
Falkreath: Grimassi, in Dead Man's Drink.
Solitude: Penczak, in the Temple of the Divines.
Dawnstar: Blavatskh, in the Windpeak Inn.
Markath: Moura, in the Hag's Cure.
Morthal: Buckland, in Highmoon Hall.
Riften: Cuhulain, in Mistveil Keep.
Windhelm: Valiente, in the New Gnisis Cornerclub.
Winterhold: Starhawk, in the Frozen Hearth.
A cookie for anyone who recognizes where I got the names for the new vendors.

I also discovered while playing yesterday that if you are using the Animal Friend mod, the natural predators will join in fights to help you, if they are close enough. Primrose was mixing it up with some Thalmor, when a wolf suddenly turned up and leant her a helpful fang.