Cheap source for 3-way syringe taps?

[ffutures]

I need to build a class set of respirometer apparatus for A-level biology. Most of it is relatively straightforward, rubber bungs and capillary tubes etc, but I also need a lot of three-way syringe taps - basically, a little T-junction which allows you shut off one of the three arms. They used to be relatively cheap, I think about 25p the last time I wanted some, but I've only got a couple left and they are now £2.00 or more each from the licensed bandits we call educational laboratory suppliers. I'll need 30+ so if possible I want to get them cheap. Does anyone know of a source?