I'm looking for series where a trap or traps are interested in a boyish girl, preferably either finished or actively scanlated.

I've already read Himegoto and Boku to Boku

are you looking for your transgender person, a girl who's dressed like a boy, or a boy who's dressed like a girl?

If it's a man cross dressing I'd suggest:

Piano no mori - not really about cross dressing, but there is a 25+ chapter section in the middle where the mc has to cross dress to play piano at a bar and starts dating a girl he meets there.
Jelly fish princess - not really transgender here, but the male leed does cross dress for fun and to piss off his family.
Usotski Lilly - don't know, haven't read, but I think mc cross dresses

Surprised no one suggested Otonari Complex.

The main guy crossdresses and is in love with his childhood friend, this girl who is a huge tomboy.