Get a good broker
JTinKy
You may want to look in your local yellow pages or on line for a broker familiar with the needed processes and compliance requirements. You might try Expeditors International or DHL Customs Compliance for a start.
Important for the seller to comply with their country's export laws and accept responsibility for doing that. Potentially a bunch of stuff involved, also need to designate who is pay freight, insurance, duties, license fees, etc. Usually covered by stuff call INCOTERMS (broker can fill you in).
A good one will help you decide what port of entry to use to minimise grief, like previous persons have comment, not NYC or DC. One issue is some of the smaller ports have more time on their hands, so more time to scrutinize things.
Real horror story, broker goofed on a bill of lading (ocean number) on customs entry documents. Customs automatically slapped a $100K fine on the importer, becomes your job to clear with customs. And they can take their sweet time in working with you to get the fine YOU own cleared up. A good broker will take care of this, but it is your responsibility in the end.
Responsibility is with the importer of record, which would be you.
Be certain to get an awareness of all the duties, freight and brokerage costs in advance from whoever you are working with, and make certain they are familiar with requirements of importing firearms.
Not trying to scare you off on doing this, just want to create an awareness of what may be involved. Good forwarder/broker will make this easy.