Solenoid valves in series or parallel?
If the valves are designed to be operated on 120 VAC, you should connect them in parallel.  If they will always be operated together, they can be controlled by the same SSR. (If you connect the solenoids in series, each solenoid will only get 60 volts, and will probably not work.)

If you want to control the valves separately, you shouldn't need another 24 volt supply - you can connect another switch and SSR to the power supply you already have.