I am in the UK so not faniliar with sellers in the USA but any electronics supplier should have something.
What size you will need I have no idea but you can work that out from the power and voltage of your router, ie P=1V so divide power (watts) by voltage and you get the current, just need to pick a relay that can handle that current at that voltage. You want a 5v coil on the relay and you hook it to a spare output from your breakout board. You may already have a relay on the breakout board, some have them some dont, do you know the make of breakout?
Hood