i couldn't find any at lee valley. i liked some of their card table and piano hinges but couldn't think of how they would work for me. if you can get those to work, please post the pics, then i will remove mine and copy yours. i don't love the drop leaf hinge. it is a little bulky. i'd rather the card table hinge and a swing out arm or something. it will be nice to see what you come up with.
I picked these up at Lee Valley today. # 00T0415 2 [at]$6.90 each ($15.59 incl tax)
The three photos show it opened at 90 deg and then straight out to release the locking mechanism and the last one shows it closed up. There is no lock to hold them closed but seeing as how a small magazine will keep them closed, the weight
of the extension counter should be more than enough to hold them closed. Friend at work has an old butcher block counter that he is going to bring in next week so I can cut it up to make my extension. I can let you know later on how they work but I don't see any problems with them.