I understand. The marketplace gateway has to work in the general case where there are many customer payment gateways.
I don’t know whether there are good fiat payment gateways for firearms. You’d have to research their terms of use.
There are articles listing payment processors who are suitable for selling firearms: https://www.cardpaymentoptions.com/credit-card-processing/gun-friendly-merchant-account-providers/
And out of those, some seem to have WooCommerce payment gateways, for example: https://pledgedplugins.com/products/payline-data-payment-gateway-woocommerce/
You would still want to distribute commissions to the vendors via some form of cryptocurrency, since none of the options available in WC Marketplace are suitable for enabling the sale of firearms.
I have been making progress on a turtlecoin adapter, and you should be able to use a2coin in a couple of weeks, if all goes well.
Perhaps you could consider accepting other more generic cryptocurrencies to attract more people. I am not sure what the merits of sector-specific cryptocurrencies are, even though I’ve read a few articles about them.
with regards