Me and my little brother have been doing an Emerald playthrough and when we both reached Rusturf tunnel, we kept finding Whismurs - which I believe is normal because Whismur is a really common thing in Rusturf tunnel - but so far we have only found female ones. We've only found the males once or twice - no more than that.
I mean, I believe that Whismur has a 50/50 gender ratio?
In the tunnel, only Whismurrs can be found. There is nothing that states it is gender locked. If you are only encounter females, then that can only be blamed on one thing, RNGesus, or rather, RNCeus
Source: Experience and this https://bulbapedia.bulbagarden.net/wiki/Rusturf_Tunnel
From Pokémon Emerald onwards, if a Pokémon with Cute Charm is in the first place in the party (even if fainted), there is a 66.7% chance that the game will force an encountered Pokémon to be the opposite gender to the Pokémon with Cute Charm if it can be that gender.
source Of course, if your first Pokemon doesn't have cute charm, then I don't know the answer.
