Well Toxicroak would have to be female to breed with Hitmonchan, though it should be noted that the egg will be a Croagunk. With Ditto Hitmonchan should breed perfectly. As long as it does not say that they "Prefer to play with other Pokemon" they will eventually produce eggs just be patient.
Remember that they only lay eggs while you are walking. There is a certain percentage of them laying an egg after a certain amount of steps.