It depends on how fast your snake grows. I got a snow corn at the end of April, it was about 4-6 wks I think, I started feeding two pinkies a week, every three to four days and I did that for a couple of months. Then I started feeding him/her small fuzzies once a week, since he/she had shed twice already, now I'm at a large fuzzy/wk.
It's recommended that you feed a meal that's 1 1/2 the size of the widest part of your snake. If it's bigger than that, your snake might regurgitate even if it was able to swallow.
I think that it would be safe to get 2-3 months worth of pinkies if your getting it in bulk, then reassess after that. Even if your snake is big enough for a fuzzy after two months you can still feed it two pinkies at one feeding until you're finished with your supply of pinkies, then restock with fuzzies.