Dan;

Nice radio from the late 30’s.
I guess the first question is: has one of the 2 coils on the speaker failed. If the field coil which is acting as a power supply choke is OK then there is no reason for you not to re-use it ( perhaps temporarily – disconnecting the speaker voice coil leads ) and connect a 4 ohm speaker to the output transformer. If you are concerned about the 4 ohms instead of 5, put a 1 ohm , 10 watt resistor in series with it to bring the speaker load to 5 ohms.
If the field coil is fried then you can replace it with a fixed inductor. Hammond , for one makes them. You will need one that can handle at least 50 to 60 milliamps , as the 6L6 ouput tube can use most of that current and there are a couple of other tubes fed thru that choke.
Instead of the replacement choke you can use a power resistor of the same value , 815 ohms. It should make the dc voltage very close but you will lose the filtering effect of the choke.

This is just a couple of suggestions for temporary fixes, that will put your radio back on the air until you get the proper speaker.

Hope this helps. Regards John G.