So the forward/reverse arms are part number LOSB4203.
The linkage is just a plain 2mm link. They dont seem to have a part number to buy one that I can find, but you can go on ebay and buy some 2mm linkage wire
HERE. Dubro makes a bending tool for $15 that will help you put z bends in the wire if you like,
LINK. The distance between the hole on the trans arm and the hole in the servo horn is 53.25mm to help you get it the right length.