Do you have seperate flowering/vegetive rooms? If so this is what I would do:

1. Take clones (cuttings) from all your un-sexed plants. Plenty of cloning guides around if your unsure how to do it.

2. Once your clones are rooted, flower them under 12/12 light to determine sex. Make sure you mark all the clones so you know what plant they came from, then you can get rid of your males and use the females as mothers for more clones

Of course this won't work if you only have the one room, although it doesn't take much space for a veg room.