I've heard of them Neil, some farmers south of town bought one together, though I don't know specifically what brand name they have. I spoked to one of the owners of it, he felt that although the kill rate was 99%, it's a very labor intensive apparatus, takes three guys to cover any significant area in a day. 1st guy with gopher balster, 2nd guy with a shovel to block surrounding holes for maxium concussion and 3rd to drive towing vechile.
I have over 6000acres of pasture/hayland/cropland infested with these varmits, grain mixed poison put out with an electric 2" auger drive dispencer on a quad takes me a wk of 12hr days to paint the farm once with a tablespoon of poison @90% approx of the holes.
I saw this outfit at a farm machinery show a few yrs ago.
http://www.gophinator.com/
With a bit of research about it shortly afterward, the closest dealer for anhydrous is 150miles away, but it's likely they wouldn't sell me small quantities b/c apparently anhydrous ammonia is an ingredient for methamphetamine. So if it weren't for the meth head druggies, I'd probably try this for a more effective rodent control tool, it'd likely be 2-3 times quicker than the gopher blaster.