The Surrogate has the authority to appoint an administrator of an estate.  If you are appointed administrator, you are the fiduciary for the estate and may be required to post a surety bond, pursuant to New Jersey statutes, particularly NJSA 3B: 15-1. The purpose of the bond, which is based on the amount of the assets, is to protect the heirs and creditors of the estate.
A bond is not insurance. You are responsible for any losses which cause the surety to make payment on your behalf. The Indemnity Agreement is your promise to repay the surety. The law establishes minimum terms and conditions for indemnity and collection, which must be in each bond. The other terms, such as premium and duration are between you and the bonding company.
You are free to purchase the bond from any qualified source.  The initial premium is due when the bond application is completed and your appointment as administrator will not be granted until the bond is received in the Surrogate's Court.
The bond does not terminate at the end of the first year.  Annual premiums are due to the bonding agent each year until the estate is closed (the accounting, Refunding Bond and Release forms, and tax waiver(s) from the state of New Jersey are all filed in Surrogate's Court).  If you do not notify them and provide proof that the estate is closed, you will continue to be billed each year for another premium.