Research and care for those with PLS comes from two sources, basically:
ALS-centric groups and places: local ALS clinics, ALSA chapters (some do, some don't accept PLS patients), etc
Spastic para/quadriplegia-centric groups and places: Spastic Paraplegia Foundation, etc
I'll write this up better for the sticky, but basically some docs look at PLS as a lesser form of ALS, some view it as a greater and less genetic form of HSP. This is true of researchers as well as clinical physicians. Both are pulling for us, and the symptomatic treatments are the same regardless. So which you go to only matters if you need to get help from a government organization like the VA that will give much better benefits to someone with a PLS (a form of ALS) diagnosis rather than PLS (a form of spastic plegia).
So PLS isn't just an orphan disease in the traditional sense of the term, it is an orphan whose adoptive parents have weird custody agreement!
For friends and family, I think the SPF's run down is a pretty good resource:
PLS « SP Foundation SP Foundation