The only dealer that has them, and it's where I got mine, is
BicycleBuys.com. I emailed Origin8 a couple of months back when I was having difficulty finding them and they told me production would resume in September. The Supercell's twin is the Chaoyang Sandstorm, which you can purchase from Moose Bicycle in Canada. Not sure if they're actually the same tire or not, but they look identical and they're both 30 TPI wire bead. Very easy to mount by the way. You won't even need tire levers. Just take your time airing them up and keep checking to make sure it seats evenly all the way around. Recommended PSI is 10-20. I keep mine between 18-20 for the street.
Now, if you need something for a mix of trail and street I would consider the VeeRubber Vee 8 as
@mrgold35 recommended or the Specialized Fast Trak Fat. In the article I referenced in my previous post, both tires were well-rated overall but especially for puncture resistance.
Finally, another tire that has been mentioned in EBR is the Vee Tire Speedster, which comes in 26 x 3.5. I've seen this tire mounted on some analog fat tire bikes at my LBS and they looked impressive. Would love to take one out for a spin to see how they roll. Whatever you end up getting, consider adding a tire sealant like Slime, Stan's, etc. Everyone has their personal preference for sealant brand.