these carbs once and a while pop up on ebay. It is difficult to get single parts anywhere (especially at reasonable prices).
Backfiring from the carb normally indicates too lean a mixture. I would suggest you also check the ignition before you retry starting her.
As for the choke: You will only need it when cold-starting the old lady. So as long as you do not have a working mechanism, fixing the choke valve in a somewhat closed position while she is warming up, should also do.