I've got a list going. I started from 1995-present. The year is when the team moved to six-man from 11-man. If there is not a year beside the school, then the school (to my knowledge) has been playing six-man since the 1995 season.
Abbott Panthers 1998
Amherst Bulldogs
Anton Bulldogs 2011
Apple Springs Eagles 2005
Aquilla Cougars
Aspermont Hornets 2001
Avalon Eagles 2005 (were not playing foortball previously)
Balmorhea Bears
Blackwell Hornets
Blanket Tigers
Bloomburg Wildcats 2010 (were not playing foortball previously)
Blum Bobcats 1996
Borden County Coyotes
Brookesmith Mustangs
Bryson Cowboys 2000
Buckholts Badgers
Buena Vista Longhorns
Bynum Bulldogs
Calvert Trojans 1998
Campbell Indians 2012 (were not playing foortball previously)
Cherokee Indians
Chester Yellow Jackets 2010
Chillicothe Eagles
Coolidge Yellow Jackets
Cotton Center Elks
Covington Owls 1995-1999, 2008
Cranfills Gap Lions
Crowell Wildcats 2004
Dell City Cougars
Eden Bulldogs 2006
Evant Elks 2009
Fannindel Falcons 2004
Follett Panthers
Forestburg Longhorns 2007 (were not playing foortball previously)
Fort Davis Indians 2002
Fruitvale Bobcats before 1995-97, 2000-2004, 2010
Garden City Bearkats 2004
Gold-Burg Bears 2004 (were not playing foortball previously)
Gordon Longhorns
Grady Wildcats
Grandfalls-Royalty Cowboys
Groom Tigers 1996
Gustine Tigers
Guthrie Jaguars
I've only gone through the schools A-G at this time.