I was at ACOS Ikebukuro three days ago (it has moved to floors 1-3 of the old Otome Road Animate) and about 1/3 of the costumes were male. The male costumes on the racks were in women's sizes, but men's sizes were available. You just have to ask. There are two picture catalogs sitting out on the 2nd floor full of costume sizing information and show costumes that are available, but not on display. Even most female character costumes were available in men's sizes.
Just when 75% of all cosplayers are women and about 90% of all cosplay store costumers are women you predominantly get women's sizes on display regardless of character gender. Cospatio (the expensive place, go figure) is about the only place that regularly carries men's sizes on floor display and even there I've had to have them request stuff in from other stores.
I need to go through and recheck all the store status's and check out a new store before updating the list anyway (like how ACOS Ikebukuro moved). I'll pay close attention to male/female size ratio when I do my checks and note those stores that have a higher number of men's sizes out on display.