This question should only be attempted by someone who is familiar with
the process of the US Navy granting concessionnaire status to a
vendor.  Please do not just "give it a go"- we need someone who KNOWS.
Our company markets personalized jewelry items to the US Military.  We
have contracts with the Marines and the Army, and we want to also
become concessionnaires to the US Navy.  How would we go about this,
where would we find the necessary forms, and what criteria do the US
Navy consider when granting or denying concessionnaire privileges to a
vendor? Are there consultants available to make the passage of this
approval go smoother?  How much will we pay in commission to the Navy
Exchange?

It always amazes me; why openly ask the question?  Go to the source.
Call the Navy Exchange Headquarters and ask them or visit a nearby
Navy Exchange and talk to the manager.