My two go to places for coils are VaporBeast, and Sweet-Vapes  LInks to follow
http://www.vaporbeast.com/
http://sweet-vapes.com/tanks/smoktech/smoktech-coils/tft4clapton-coil.html
I bought my wife 2 packages of
"authentic Kanger Coils" off of ebay for her subtank nano, The first package was great, each lasted a long time, vaped clean and fit perfectly in the tank.  The second pack seemed off somehow. they didn’t fit easily when installing them.  I had to sort of push real hard on them to reach the threads. they lasted less than a week before beginning to taste a little harsh.  Wifey vapes at about 38 watts, on  a Kanger subox nano, a  Vapresso Target or an IPV mini 2.  Shouldn’t be a problem.