I cannot answer your question directly about the coil voltage, but here are some tips that may help.
Relays like power transformers, the physical size determines how much power they will handle, meaning the contacts. As a result the coil is made accordingly. If you measure the resistance of the coil with an ohmmeter and look in a disributor catalogue like mouser for a relay with nearly the same physical dimensions and look for a similar coil resistance. You just might find the answer. The higher the risistance the higher the coil voltage.
Relays like resistors dissipate power in the coil. The coil voltage is generally close to the maximum voltage. Most relays will energize at a reduced voltage, and most will stay energized if once energized at the specified coil voltage and then the coil voltage is reduced, sometimes this can be over 50%. With DC relays the coil current is a direct relationship to ohms law. Coil voltage/coil resistance= coil current. Coil power = Coil voltage x Coil current.