I found something similar here :
I looked at the data sheet, the relay is specially made for switching transformers in microwave ovens. I think this is the case because of the high voltage sparks the contacts can handle.
But i looked at the website of omron as well.
It seems the model you have may no longer be manufactured. I had in the past some experience with Omron and the company i worked for had some serious quality issues with omron relays in the past. Perhaps the G5G had some quality issues as well and was later superseded by a better and improved design. And marketed as a cheaper process
I think that as long as you have an relay with a contact that closes when the relay is powered, and the contacts can handle at least the same the power switching requirements and the coil voltage is the same you can use the relay. I think the best and cheapest way would be to just salvage an old magnetron oven that still works. The basic function of all these machines are the same. The user interface is just different. For example buy a second hand magnetron on ebay and use it for parts.
One of these might very well do the trick.
This may be the best choice relay from omron, you need to do some modifying though...
available at mouser but the price is insane, maybe it is wrong :
I have difficulty determining what voltage the coil is of the model you want to replace. Does it say 12 Volts or 24 Volts. 24V seems to be more common.
Could you check please ? A 24 Volt relay will maybe switch on 12 Volts but the contact resistance might be higher because the force to close the contacts is lower and because of that the contact can burn in and degrade faster. Usually these relays switch a transformer. As such, the contacts have to withstand a lot of punishment. Even with the rated voltage i think you need a relay that is specially designed to handle the currents and the high voltage sparks caused by the induction voltage of the primary coil of the transformer which feeds the magnetron tube.
Here is some background information :
Added this quote from the link above from page 5 :
At low voltages the relay contacts behave normally, but at high voltages they can no longer be considered as contacts but as a moving spark gap.
For those interested in the principle of the magnetron :
And to find replacement parts :
NO or N O= normally open, NC or N C = normally closed.