The only players you will accept in place of Barry are Nocioni, Jax, Barnes or maybe Posey? Prepare to be disappointed.
Nocioni is a longshot. Nellie loves Jax too much to let him go. Barnes only will sign with California teams. Posey is the most possible but also the least exciting out of that group.
Mickael Pietrus is possible if he gives the Spurs a hometown discount because of Tony Parker.
But really, this is a bad FA summer for the Long Three the Spurs have needed for years. If they didn't find one in the best when there were plenty available, I don't expect them to find one this summer.
Perhaps the draft, but I'd be happy with a Devin Brown or Ime Udoka type player given the shallowness of the FA class.