Unfortunately there isn’t a simple answer as each state, province, and country has their own rules. In Canada each province requires a different document and this will likely require the stated clerk of classis to have some official communication with the appropriate government department. (In Ontario it will be the Canadian Ministry Director rather than the Stated Clerk.) A great place to start is with the provincial office. Leave yourself a bit of lead time to get everything in order.
In the USA a good place to start is by contacting the office of the county clerk where the wedding will be held. Some states may require extra documentation, and some will not.
For countries outside of the USA or Canada you will want to find a relevant government office to contact.