Unfortunately, I don't have the original brakes.
So last night I tried on half a dozen different sets of canties and V brakes from a 1990 Trek 800 to a 2010 Mongoose hybrid. A couple wouldn't allow enough vertical adjustment, the others would.
The problem is that the Myata has 60mm spacing between the front forks, whereas all of the other bikes had about 80mm spacing. The result is that in order to make them fit I have to rotate the brake arms outwards. This, in turn, means that the brake pads aren't square with the rim's braking surface.
I have seen these old school Dia-Compe cantilevers for sale online.
I don't know what model they are. Anybody know if they would be worth a try?