How to schedule H4 visa appointment


I am currently in US but my wife is in India. I am trying to get H4 visa stamped for my wife but I am not able to schedule it. Even my employer is not able to get an appointment as in their website it mentions “There are currently no appointments available”, but I am seeing in different groups that people are actually able to get slots, if not a regular appointment at least EAs are getting booked. I am trying to get the appointment booked in Kolkata.
The questions I have is…
a. Is my case eligible for emergency appointment?
b. Which is the best immigration agency/website I can seek help from to get an appointment slot?

Thank you!