Some are:
Citizens Committee for the Right to Keep and Bear Arms, a lobbying group, Liberty Park, 12500 N.E. Tenth Place, Bellevue, WA 98005
Second Amendment Foundation, an educational group (contributions tax-deductible), James Madison Building, 12500 N.E. Tenth Place, Bellevue, WA 98005. (SAF is associated with CCRKBA.)
Gun Owners of America, a lobbying group. (Sorry, I don't have the address.)
There is also your state rifle and pistol association. If you belong to a gun club which is "above" engaging in politics, try to persuade them to be more active.*
None of the above has the clout of the NRA, though. Being able to speak for 3 million members is much better than being able to speak for yourself and your brother in law.
* A "bennie" to belonging to a state association or a CMP affiliated club is that membership is a prerequisite to being able to purchase rifles through the Civilian Marksmanship Program.
Jim
Jim