Costco has nitrogen at most locations, I think. There is a dealer locator at the
Get Nitrogen Institute that can be helpful. It doesn't list every place that has it, only those who are members of the Get Nitrogen Institute. St. Lucie Tire and Battery in Ft. Pierce has it, I know that because I had my tires rotated and filled there once.
Mainly, just ask a local tire place if they have it, and if they don't they will usually know who does. Those who don't have it tend to say it's a load of crap and doesn't work. Don't listen to them. It probably won't make much of a difference to someone who lives and drives locally, not putting a lot of miles on their car annually, but for someone who puts a lot of miles on theirs like we do, it's money in the bank.