I always try and source different Scarus but they can be problematic shippers from certain export locales. The most common Pacific species exported is the juvenile Cetoscarus ocellatus, followed by S. quoyi, then infrequently Chlorurus bowersi, Chlorurus bleekeri, and Scarus chameleon. I personally think the biggest issue is that most export stations overseas have a difficult time positively identifying these fishes, and just offer them up as "Colored Parrotfish" which complicates matter further.
As far as female Quoyi, I have received a few small ones (3" specimens) which appeared to be females, but its very uncommon see them offered at this smaller size.
From my personal experience, combined with a close friends who has a very large home aquariums (1000 gallons) and tried to maintain a larger male and a few very small Scarus quoyi together, it didn't work out well. After adding the small group within days, the male was relentless and would try and kill the two smaller fish of the group. I dont think mixing different species of larger Parrotfishes works well either, even in very large home aquariums of 500 gallons or more.
Kevin Kohen