I want them in large, respawnable quantities.

Everywhere. Literally everywhere. But check out the links below, I did a quick search on the wiki and found this, you may find them helpful.

http://elderscrolls.wikia.com/wiki/Blue_Mountain_Flower

http://elderscrolls.wikia.com/wiki/Blue_Butterfly_Wing

As some idiot said ...

You cab find an abundance of them in Whiterun Hold.

They are everywhere until you need them, just like deer.

Just like anything really

It wouldn't hurt to check in with the alchemists around Skyrim. If you're in a rush, fast travel to each of the Holds with an alchemist and see if they have any of ingredients you need for sale. Do a full 360 of Skyrim and by the time you're done, 48 hours should have passed and you can repeat the process.

Of course it's so much more fun to go out and find the ingredients yourself.

I actually did that. They have AT MOST 1 of those ingredients, which is really slow. If they had like, 10 at least I would keep at it more, but no. I hate sitting behind a loading screen repeatedly only to find the shop doesn't have the ingredients I want. So I wonder if there is any place to find them in large quantities. Also, I went to those places on the wiki. Couldn't find the butterflies. Damn.

If you have Hearthfire you can grow them - both. Well, the butterflies just float in from no wheres when you grow flowers in the (optional to build but silly not to choose it) green house.

Well I don't have Hearthfire. I DO have Dawnguard though.

Blue mountain flower is all over, on the side of any road you travel. It is more in some areas than others.

Blue butterfly wings are great at the trail going to the vampire lair outside of Morthal, and also look for them around signs, and also outside of Solitude.

http://www.uesp.net/wiki/Skyrim:Blue_Mountain_Flower

http://www.uesp.net/wiki/Skyrim:Blue_Butterfly_Wing

There are respawning butterflies in the greenhouse (Hearthfire) and Riften (go in and out of the orphanage and run to the Talos shrine). Blue mountain flowers tend to be most common at relatively high elevations (not too high or all you'll find are snowberries).

Just thought I'd mention that butterflies appear between 8am and 8pm, lunar moths, torchbugs between 8pm and 10pm. And none of them will appear during inclement weather, that is, rain or snow. Cheers!