I have a 1967 Mustang Fastback. The switch on the brake distribution block is bad. My problem is that my switch has only one terminal and I can only find replacemnts that have two terminals. Anyone out there have any idea where i can find one?  

If it has only one then a two post won't work. Single post grounds at the switch (two post grounds thru wiring)  

Bingo!!!!! You are one of the folks that are lucky enough to need a part that ISN"T available either new or repop for a Mustang!!! You win the booby prize!!!
Seriously, replacement switches are not made for this item. I can think of a couple other things which are not available, such as the windshield wiper switch for 67/68's.
You don't have many choices---either NOS (lots of luck) or used (and who knows what you'll get when you buy used). That's why so many 67/68 Mustangs don't have the light operable. If you're fortunate enough to be able to get it apart, maybe someone who's a electronic geek can repair or rebuild it, but don't get your hopes up, If it were easy to do there'd be all kinds of write-ups about it  in the Mustang books!
Sorry I couldn't help more; Ive had 4 67/68 Mustangs over the last 35 years and none of mine worked.
Jay67fast