are you talking about the breaker panel or the Transfer switch
the internal parts are usually MFG only BIG lot items, not individual pieces you buy off the shelf
your best option might be to over to Rice Ranch to the RV accessories dealer there
the back room under the tent has all kinds of surplus and swapped out salvage components electrical and mechanical
find the breaker box or switch or panel that has the right size buss bar
the cheapest will be an old manual home fuse panel switch box
and buy the box, then remove and use the neutral bus in the place of the burned one
you might be able to go online and find a terminal strip/buss
but it would be a make do option
these are NOT normally individual parts
the RV guy did not lie, they don't have parts for TS repair
the whole process might cost more than its worth
you might find a used TS complete for less $$ at the rice ranch location
just inspect it closely before purchase