To answer my own question if anyone else comes looking for an answer, the Kmart ankle weights that Ben posted above seem to be the cheapest solution ($6.50) that will just reach around the ED80 dew shield.
Anything larger and you should get the one Andrew suggested above from Rebel sports.
Also I have possibly found a longer Vixen-style dovetail bars,
400mm long here for example. However, I am not so sure about the stability because of the long cut along the length.
everybody!