The old 21.
Shimano Deore DX cantilever break, BR-M650. 6€ plus shipping.
The new 21.
2 sets (4 pair) of Shimano Deore DX cantilever brakes, BR-M650. 20€ each set plus shipping.
& 1 pair of Shimano Deore XT cantilever brakes BR-M734 (new pads & cable clamp needed). 9€ plus shipping.