We got ours from Modaz, so you could try him They are the penplax ones. Although quite clear to start with, they do go opaque quite quickly so the males can't see each other so well.
We also used the black flat edged paper binders which you can get cheap from most stationary shops to slide the divider into. They are just stuck in position with aquarium sealant.
I got mine off ebay I have a 28L Aqua Start 320 which i divided into 2 much like Netty it houses two males Otherwise you can pick up a divider from the pet store. I had to cut the plastic to tank size which was interesting and also put a plastic cover on top of water and under the lid as mine tend to jump.