Moving jumper tabs to change input voltage on Syncrowave 300 welder

Gentlemen. I recently acquired an old Syncrowave 300 welder at an
auction. It is currently set up for 460 volts single phase. This
setting involves one copper or brass jumper tab that join terminals 3
- 4 of 6.
To change the voltage inputs to 230 volts 3 phase requires 2 jumpers.
One connected to 2 - 3 and another connected to 4 - 5. The normal
protocal is to piggy back two jumpers together when they're not
needed. However, somebody didn't do this and therefore, one jumper is
MIA.
These are simply thin tabs of copper or brass. I'm wondering whether
these are a purpose built Miller item or can be bought from an
electrical house or even custom made.
Anybody have a clue? These are much thinner than the bars used on a
Syncrowave 500. They're just thin sheet material.
TIA
Vernon