At this point I don't think the Patriots will sign a veteran free agent free safety - and I'm warming up to the idea of Jonathan Jones in that spot. Regardless, here's a list of those with any starting experience at the position that are still available.
Justin Simmons, 30, Denver; 2x Pro Bowl, 7 year starter
Eddie Jackson, 30, Chicago; 2x Pro Bowl, 7 year starter
Quandre Diggs, 31, Detroit; 3x Pro Bowl, 7 year starter
Micah Hyde, 33, Buffalo; 1x Pro Bowl, 8 year starter
Tracy Walker, 29, Detroit; 3 year starter
Marcus Maye, 31, Saints; 4 year starter
Adrian Phillips, 32, Patriots; 1x pro Bowl, 4 year starter
Tashaun Gipson, 33, 49ers; 1x Pro Bowl, 11 year starter
Julian Blackmon, 25, Colts; 3 year starter
Keanu Neal, 28, Pittsburgh; 1x Pro Bowl, 3 year starter
John Johnson, 28, LA Rams; 5 year starter
Will Harris, 28, Detroit; 2 year starter
Justin Evans, 28, Philadelphia; 2 year starter
Rudy Ford, 29, Green Bay; 1 year starter