from all the artists that I know of, here are some that fit into this.
Bmage: he has no problem doing male and female weight, he just takes a while in doing it.
Saxxon/Saxxoff: you can pretty much give anything to this guy and he will do it.
Countessfayt: she loves Male weight gain a lot but is okay with doing female weight gain as well. she has not been active in a while.
Antioxidated: Male and Female weight gain is her bread and butter. not too sure if she does shota or loli
but I could ask her.
Serioinc: no problems with it but not going to happen any time soon.
Gain-Over: well known for female weight gain, asked him if he can do male weight gain and he said yes.
I can think of others but most of them are furry