You might try some olive oil, if it is a blockage of the crop but you must be very careful administering it. I've never tube fed a quail before....so I can't really help you with that but I'll tag the Expert on tube feeding, she can most likely help you with it.
@casportpony , get you give a...
The only thing I know that ACV is good for is to help alleviate some of the symptoms of sour crop.
I never have had a quail with sour crop but I have had a few grouse that had sour crop, and ACV is what I used to help with the symptoms.
I have also used Micronazole.
Here's an article about sour...