I don't have the Gumbo's, but do have the Buckshot Mudder Radials in 305/85R16. Was able to get them through my local Discount Tire Store. Their price is close to what National Tire sells 'em for, but you can get a warranty & lifetime rotating & balancing as well (that's a big deal w/ tires this size). I think the closest Discount Tire to you is in Northern Utah. How much trouble you have (or don't have) depends on their knowledge, but it can be done.
Your best bet may be to query your local independent tire dealers & see if they can get 'em thru a regional distributor. I used to work for a couple shops like that (in small mountain towns) & you might be surprised by the price & how easily they can get 'em. One thing to note... make sure they DON'T order them thru Premier Tire Distributors in Denver. I've been screwed several times by Premier b/c they quoted my tire dealer one price & charged another or told my supplier they had tires in stock they didn't have & worse wouldn't get or even try to get. Their attitude there seems to be if they can't make a really good profit on a tire, screw it & the customer.
Big O tire can be a good source depending on the local store manager. I've had stores that wouldn't even try to get the tire, others who would, but make ya pay thru the nose & others that would go out of their way to get me a good price. Your mileage may vary. I see they have a few stores near you.
Personally, I like the Buckshots b/c they can be studded & I can get 'em in a 10 ply. They self-clean pretty well (not as good as Swamper Boggers) & are a lot better on the road than either Boggers or Gumbos. They are also narrow enough they can be run on a dually if you use narrow rims or a small spacer between the rears. We live roughly midway between Laramie, Cheyenne & Fort Collins (near the I-80 summit) & can get snow 12 months of the year. Our last snow was June 6th this year. We frequently drive into the higher mountains & get a lot of icy roads so I run studs year round. BTW, I run the Buckshots on my '71 Chevy K20.
While the BFG MT & Swampers are great in mud, they are next to worthless on ice & hardpack snow, which is where the studded Buckshots really shine. The Buckshots do really well in deep & extremely deep snow, too, when studded. The stud noise is noticeable, but not blantantly so.