I found these two sights; they make it exceptionally easy to donate money to the NRA and GOA. Memberships are great, but donations are just as good. You can donate anything from $10 or $15 to more.
https://www.nrafoundation.org/donate/donate.aspx
http://gunowners.org/paypal.htm
http://gunowners.co/contribution-000
https://www.nrafoundation.org/donate/donate.aspx
http://gunowners.org/paypal.htm
http://gunowners.co/contribution-000