What about sensory processing disorder (SPD)? Where are the SPD adults and SPD support (for those who have it and parenting support)?
For starters, there is the SPD Foundation, incorporated in 2005. I'm not sure how high its profile is at this juncture, however.
As for support, I see two obstacles. First, SPD is not formally recognized as a diagnosis. Second, those who do diagnose it (mainly occupational therapists) haven't been doing it for long, relatively speaking. As noted above, the SPD Foundation incorporated in 2005, whereas autism support has been around for much longer. SPD support simply isn't evolved in part because it hasn't been around that long.
As for the lack of adults with SPD, perhaps that's in part due to the novelty of the diagnosis and in part to the affect of maturation on SPD. By the time adulthood sets in, perhaps the condition has lessened or the person has learned to adapt? Just guesses. In the next ten years or so, perhaps adults might start identifying as having sensory processing disorder? But as of today, that doesn't appear to be the case.
Added: As Kris points out, SPDLife is a resource dedicated exclusively to adults with SPD.