The Experimental Soaring Association sells some of the published books and materials from Stan Hall. They will know whether the plans are available and where.
The president (and high exalted righteous iron-fisted fearless leader) of ESA is now active on this HBA forum, username MV4440 or something like that.
If you can't find him looking through recent posts in the Soaring or Sailplane discussion sections of this forum, shoot me a PM and I will forward it to him or call him personally.