Just take your business elsewhere.
Consider a form letter to the manager of such places telling the manager that you have been a customer for a long time, but cannot, in good faith, do business with anyone who would put politics and political correctness over the safety of its customers by not allowing them to defend themselves.
On occasion I have gone through the effort of asking a manager about signs when I have seen them. At two places (Gander Mountain and a Wireless service and device store) I was told that those signs don’t pertain to law abiding customers who have concealed carry licenses. When I asked who the signs are for then, it seemed to occur to them, quite spontaneously, how ridiculous the signs were.
“So you have those signs up to deter criminals from bringing guns into your store? Is that the purpose? Isn’t that like posting “no swimming” signs at pools to deter fish from swimming in them?” -— I actually used that line and will continue to do so. I’m so clever. :o)