Source of large quartz crystals - Brazil and Hot Springs, AR come to
mind. Coleman mines quartz in Arkansas and does find very large
crystals - clarity may be an issue.
Ron Coleman's site is under construction:
Over 20 years ago, Ron helped us out with a very large crystal for a
special "hands on" exhibit for children and the blind. The specimen
was opaque but he may be able to locate what you're looking for.
Jim Coleman Crystal Mines, Inc. -
Though none shown here are approaching 4 feet, he may be able to
source something larger. There are some large water clear points
listed under Arkansas Clear Quartz Points:
"Collier Creek, new find"
"Special, McEarl, etc."
Someone who has obtained VERY large clean crystals is Lawrence
Stoller. He may be able to recommend a source or possibly have
something available for sale. Lawrence Stoller specializes in cutting
and polishing very large crystals. www.crystalworks.com
See this article "To Cut a Giant" from LJ.
HTH. Good luck to you