Why not just buy all males? My daughter has an all male guppy tank and I must say it looks quite beautiful. The males seem to get along just fine with each other and thier color variations are quite stunning.
75 Gallon--Rainbow Fish Tank/Amano Shrimp
29 Gallon--Chili Rasboras/Celestial Pearl Danios/Yellow Shrimp
20 Gallon--Ember Tetras/Orange Shrimp
10 Gallon--Chili Rasboras/Cherry Red Shrimp