Junction boards are only for connecting things together. There is no big electronics on it. You should be able to repair it with a soldering iron.
SP300V was discontinued in 2009, the SP540V in 2007. Most of that companies keeps parts on stock for 10 more years. It will be hard to find such specific parts, except you will find any defective printer to buy for small money.
but frank, can't he substitute a small bg of wire nuts or chicklets?
setting aside for a minute the fact that i don't see what can't be repaired on the existing board