I've lived around the border in Texas and Arizona on and off for three decades and my old boss runs a newspaper in the Big Bend country. I pay attention to such things, but I've yet to see a sheriff's department in the area with jeep-mounted recoiless rifles.
And if you don't think that they're available to the banditos, you've not been paying attention.
As I stated, if they do not have them it is only because they do not really want them, or have not made any sincere effort to get them.
But complaining about the lack is good for political sympathy.
Even our local ski lodge has a couple of recoilless rifles, they use them for avalanche control.
L.E. is exempt from the 922.(o) prohibition on acquiring or manufacturing new NFA items.
But as I also noted, having them does no real good if they are afraid to USE them.