21 speed means you need a set of 7 speed shifters, which can be tough to find but likely not impossible to find on ebay. Alternatively, you may be able to more easily find a set of downtube 7 speed shifters (still friction on the front shifter) and use a set of shifter mounts from Rivendell or similar. Any bar end that can be switched to 'friction' mode will also work fine.