Looking for link to Double Pole Single Throw (DPST) relay for Arduino
A relay that can switch 30A on mains voltage is not going to be able to switch directly from 5V. Getting something that can switch from 24V is much more realistic.

High amp relays are often called contactors. 4-pole ones are not uncommon for industrial motor applications. 3 high-amp poles are for 3-phase power and a low-amp one for a control signal.

You can buffer up the signal using a transistor (you'd need one anyway to supply the coil amps) or another relay.