Sorry I can't find a decent leggings specific sponsor, looks like a gap in the market there.
The Zishy site has a fair few leggings updates, always sells too, site is much cheaper to join than most which is good and bad, depends if you can get the traffic up high enough for it to be worth your while, with Yoga Pants that's definitely possible
http://www.wehateporn.com/2014/04/26...girls-updates/
http://www.wehateporn.com/2014/03/12...ls-march-2014/
Plenty of such updates in OnlyTease as well