Frank says:

If the necessary part is not commercially available, try making rivets from iron, steel, copper or brass wire of the appropriate diameter. (Order of hardness: Steel (piano wire); iron; brass; copper.)
Cut wire to length, hold in vice, bend or hammer to form first end, crimp or bend other end with pliers.
(Obviously be creative in your technique according to your requirements.)

Russ says:

I had similar problem with an old MDC kit and emailed Athearn parts. Turns out they had some sent them for free. Worth a try.