That type of well-stocked gun shop was not too likely to find on small town Texas street.
If I recall the scene in Highwaymen, Capt. Hamer inspects a Colt Monitor, a version of the BAR. That ran over $300 pre-NFA, equivalent of nearly $6000 today. Not impossible during the Great Depression, but I don’t think Colt ever even sold any Monitors to private citizens (likely just due to cost).
Even in the pre-National Firearms Act days, the cost of automatic weapons were high, making them bespoke items to order, not usually sitting on shelves. For instance, the Thompsons being used in the Capone-era Chicago area were often traced to the same suburban hardware store. I am certain there are some Colt or Thompson collectors who correct me if I have mis-stated the general situation.
That said, awesome scene. Reminds me of the LA North Hollywood Shootout where the LAPD armed with Ithaca M37s and Model 15s where unable you stop a pair of bank robbers. A few grizzled sergeants headed in the general direction - one commandeering a bank armored car and another stepping into a local gun store to hand out AR-15s like a McDonald’s drive-in window.
And if you have never read it - recommend reading Shot All to Hell: Jesse James, the Northfield Raid, and the Wild West's Greatest Escape. The main event in the book is how some unrepentant racist rebels decide to rob a Yankee bank - and a bunch of Norwegian farmers armed by a hardware store darn near massacre them. The book gets into how they hunted the escapees down.
