Don't be afraid of your python out growing the size of feeder you bulk buy. I'm feeding my 300g girls rat weanlings right now, and they both get two prey items per feeding. Which equals out to the right amount of grams they should be chowing on.
I also won a great deal on some hopper mice, so they'll be snacking on those soon two probably have to feed three to them each to equal out. But, that that's not a bad thing in my book.
As for reptile expos, I'm sure there is one near you just take some googling around to find it. Check facebook too! I'm in a bunch of reptile related groups and get some good scoops on great deals.