oops, forgot to take a screen apart, sorry.
those buttons are pretty standard and radioshack should have them.
of the 4 legs remember they are in pairs so when you solder them back in make sure you get the right or it will be like the switch is permanantly pressed. from memory (although it has been a while) i think you want the common legs at the top and the bottom - ie the top two holes int e board are the same and likewise for the bottom - but check with a meter 1st before you fit the switch.
oh hang on...will jsut check the digitalww site....
yeah if you look at this picture

from digitalww.com
then you can see the bottom legs are joined by a line of copper.