I called the National Assoc. for Gun Rights. I was told they do not do any phone calls: they use mail and email only. I found no other group using the moniker "National Gun Rights." I suspect this is a total scam.
And, by the way, the FCC has enabled this sort of fraud by disassociating phone numbers from actual geography. No phone number can be relied upon as being tied to a particular location, and the FCC generally permits the use of "spoofed" phone numbers: fake numbers generated solely for use on Caller ID. Less than ethical carriers (usually of the small independent CLEC variety) buy large blocks of phone numbers, and then use them just for the purpose of handing off calls on the called party end of things for some other unethical carrier on the calling party end. The FCC calls this "competition."