Guns and ammo are still be made at the same (or perhaps slightly higher) rate then they were before the panic. The only difference is that now instead of sitting on the shelves for weeks/months/years at a time. They are being bought as soon as they arrive. Which has booth good and bad sides for shops.
Good:
Inventory turns are almost measured in minutes, instead of weeks or months. Yes, while wants are going unfulfilled, product is going out the front the door as fast as it's coming the in the back door. Which is what every business wants, sell inventory as quickly as possible. And from various reports manufacturers are doing what they can to increase production while looking ahead to when the panic ends.
Bad:
Cash flow for smaller shops. They made their pile by selling pretty much anything and everything they had on hand. Which hopefully means that they are smart now that there's possibly less cash coming in now due to the inventory constriction. Rent/Mortage/Insurance/Salaries/etc. still have to be paid each month while they wait for the supply chain to catch up with demand. But if they are selling everything they can get their hands on, and properly managing their cash flow, they should be okay.
Getting new product.
Manufacturers sell to distributors. Distributors sell to retailers, large, small, internet and mail order. Each one probably has their own way of determining who gets what. Most are probably on some type of allocation system. Meaning everyone gets a percentage of what they ordered/asked for. That way everybody gets something to sell which will keep everyone (hopefully) in business.