B2 visa renewal dropbox appointments availability


My parents’ B2 visa has expired recently and they are eligible for the dropbox renewal process. I am working on their DS-160 forms and other required documents and planning to book the dropbox appointment in June/July.

But meanwhile, I would like to know the availability of dropbox appointments in Mumbai. Are they easily available or are they very limited?

Approaching a travel visa agent for booking the dropbox appointment would be recommended or not?