Rivarossi Heisler - the old version - part needed

I have an otherwise brand new 20 yr old Heisler that is missing a (metric) hex-head screw that secures one of the side rods to a driving wheel. Anyone have a clue where I can get a replacement? I’ve tried some of the LHSs in my area to no avail. If someone has one to sell please email me.
Thanks.
BILL

I own a rivarossi hudson dated from 1979, and after observing the screws that holds
the drive rods together, it was thesame size as the screws that held my 2002
bachmann 4-8-4’s rods together ! If bachmann doesn’t carry them seperate, you should
check for when your next local train show comes into your city. Train shows usually
sell old seperate parts for cheap.