The so-called "Portuguese Guitar" or "Fado Guitar" is indeed about the size of a tenor mandola and has twelve strings with simple screw tuners arranged in a fan on the headstock. (P.S. It's a b****r to string up as you need loops at both ends of your strings!)

They make a glorious sound and I used to have a beauty for a number of years. Good ones are fairly hard to find. I don't know the Portuguese musical instrument market at all but your best bet, as Giok mentions above, is probably Lisbon.

There is a fairly basic and relatively undecorated one for sale here in Brussels at a reasonable price. The sound isn't too bad.

mooman