Alan @ ecigarettecigar.com has always handled RN4072 kits and accessories and is a great guy to do bidness with!
Luckecig carries RN4072 kits, etc and has some different colors that I haven't seen before (at least for the Rn4072.) I've had good luck with them. I still can't figure out why more vendors don't sell rn-4072 penstyles! It's by far my favorite standard PV.
RN 4072's are the best and I get mine really cheap at mostbuying.com This is a Chinese company but they offer low shipping as long as you're not in a hurry and they sell 5 packs for $26.45
I just ordered the RN-4072 whole shebang (kit, carrying case, extra cartridges, blue foam, etc.) from myPVshop.com using the 10% off code and we'll see how it goes when it gets here!