I boycott ANY and ALL businesses that do not recognize MY 2nd Amendment rights.
How do you know who does? Sure, some folks have signs banning carry, but there are others who simply haven't posted yet
Then there are the ones who couldn't care less about the RKBA (or might even be hostile) but don't have the inclination to be too public about it. Just because my local widget store doesn't ban carry doesn't mean they don't support anti-gun organizations.
Or, how about a company that does business with other companies who don't recognize the RKBA? What if it turns out the bank holding my mortgage gave money to an anti-gun politician's last campaign?
The idea of boycotting every business that doesn't support us seems satisfying in theory, but it would be an unworkable nightmare in practice.