Polk has hosted a Border Showcase in the past. The interesting thing is while they are the host school, they play at different schools. Sometimes it may be on the SC side.
Watauga has hosted one in the past also.
Most schools here in the Asheville area seem to go head to head, 3 way or 4 teams max. Check with Reynolds.
I don't know of any in the area that do a full blown jamboree, all day event.