The smurf village contains only male smurfs and the only female smurf is Smurfette who's made by Gargamel and were artificial. The smurfs existed long time before Smurfette's existence. I'm curious at your theory to this paradox.
1. Hermaphrodite reproducing. They all can fertilize each other and being fertilized. It's a possibility they makes eggs and aren't mammals. (I borrowed this theory from others)
2. Genders are separated
Either the genders lives separated due strict traditional rules (and have only mating visits) or they lives in difference villages due work. Perhaps it's something similar to the oil platform where the workers lives at their working place a while before they goes home. The women and children lives in one village, but the men lives in another one because of work. But the women aren't mentioned in the story because they are so far away and aren't so important for the plot.
A smurfs definition at gender are what they wears, not which anatomy they have. Perhaps every smurfs who wears pants are boys, but they who sports long hair and a dress is girls.
Maybe a mutation affected their brains with a accident, so every smurfs do identify themselves with the masculine gender. But there are still two different anatomies.
Most Helpful Guy
Asexual reproduction from binary fission (Yes! They are that small!), or budding/tubers (see below). Those are my ideas, anyway.