As a general rule, marriage reqires agreement between two people and a public declaration of this agreement. This can be a verbal agreement in any mosque, at home or as a matter of fact, anywhere.
The law plays no role in any marriage, but to get the status of legally married, for the application of family laws, for tax purposes, divorce, and all other matters the marriage has to be legally registered. Any couple can walk into county office and register as a couple as long as marriage ceremony was held in the same state. If no marriage ceremony was held, I beleive both appear in front of a marriage commissioner who performs marriage at the spot for legal registration purposes.
If you consult your county office they can give you a list of people who can perform marriage and issue a certificate that can be taken into the county office for registration. Normally religious leader can perform marriages and issue certificates. Check with the local mosque. Check wit the Ghamidi Sahib’s organization if they can also perform such ceremonies.