Your best bet is to find someone on your side of the pond who buys regularly from Holts and ask him to bid for you and ship your guns with his when you have both been successful. That should produce some economy of scale even with whatever he would no doubt add for his services.

Even so with import and export licences, international shipping and other charges it is likely you will pay more to get a gun to you than it is worth unless it is of very good quality.