That is absolutely ridiculous. I'd find new banks and payment processors to work with quite honestly. If you search there are definitely firearm-friendly banks and payment processors. Why not just switch over to one of those? While you aren't actually selling anything firearm-related, it's more of a freedom of speech thing the way I see it. You've been working under the Sidearmd name and building hype around this since December 2018 when this thread was posted, if you ask me it's pretty unreasonable to be forced to change that suddenly.
and hey, assuming you're in the US, bonus is that you could then make some actual sidearmd firearm accessories if you really wanted...
It's not just the bank it's shopify too. You need to think international, it's not just about the US state of mind.