I used to think that it was a 50/50 chance of finding a male or female Pokémon, but it's not true. For example, I heard that there is only a 12% chance of finding a female Salandit (evolves into Salazzle through level up, if it's female).
This info is already displayed on each PokeDex page. In each dex page, under the "breeding" section, gender ratios are shown. So on Salandit's page here, you'll see:
These are already shown on the Pokémon's information page, under "Breeding". For example:
In fact, if you look at Salandit's page you'll see that the encounter rate of 12.5%male/87.5% female is there, right under Breeding. So we got you covered, what you're looking for is already there :)
List of Pokémon gender ratios for further reading.