As has been mentioned, there's a difference in property rights between Shadowrun and, say, D&D. For D&D, especially 3.X, while the 'official' settings and books are all proprietary material, the d20 system itself had the Open Gaming License, which allowed third party publishers to make sourcebooks and even entire campaign settings based on the d20 system, so long as they didn't actually use proprietary items, such as Bigby, Greyhawk, or Drizzt do'Urden. Shadowrun, on the other hand, has no such open license, so publishers cannot use Shadowrun's system for their own works unless they pay to license it from the property holder. In addition, because Shadowrun is a single coherent world, rather than a bunch of different campaign settings taking place in multiple worlds, the difficulties rise even further.
Long story short, you won't see Shadowrun sourcebooks from anyone but Catalyst, or the equivalent foreign companies. As for t-shirts, art, or any other such things, anything Shadowrun is going to have to be properly licensed. It is possible (people do similar things with other companies' products/logos), but it will cost money for licensing, and for a niche product of a niche product, that'll cut into any potential profits quite severely. Now, you can make art with a cyberpunk feel to it while including elves, trolls, a pyramid-shaped skyscraper in the background, and even a dragon, and that'll be some really fragging cool art. However, if that dragon looks too much like Lofwyr, or you put a corporate logo on the side of that building that just happens to resemble something from SR, then you'll start getting in trouble. That line is blurry, and usually defined by lawsuits, so it is best to keep a wide berth from anything that might appear to be infringing on proprietary material.
