Mike, the Outfitter can use most 26x3.8" tires. There are several brands that make them including Schwalbe, Surly, 45NRTH, Maxxis, etc.
The racks used are produced by Old Man Mountain. We are in the process of building a custom Lebowske which will use the same racks. The build will be completed this week and I hope to post some pics.