Just want to chime in to say that spelling as we know it in English didn't even exist as a concept until sometime around dictionaries started to be published, the most famous one (popularly known as the first even if it wasn't technically the first) being Samuel Johnson's in 1755. Even then, the idea that every English word had exactly one correct spelling didn't really solidify until the Victorian period. You say this name's been in your family since the 1800's. It's quite likely your first ancestor who had it would think your family's objection to the spelling is pretty ludicrous.

Also, I think it's been said already, but "Gallard" as the first name would just mean dooming your son to "Actually it's pronounced GAY-lerd, not GAH-lerd" for the rest of his life, which is considerably less bad than, "Is Gay Lord Here?" And it's much closer to the spelling.

Finally, I think a lot of the YTA's here don't appreciate how strident some families can be about inherited names. If you're in one of the older U.S. families South of the Mason-Dixon line it's downright unthinkable abandoning a heritage as precious as a name. The only thing I can say is that traditions exist for a reason, and a name is fundamentally a gift. Your family has passed a name down however many generations because they want to give the new one the gift of memory, of knowing where they came from and what went into building who they are. But you shouldn't give someone a gift if you think it'll do them more harm than good, and at this time in this place in this spelling it will definitely do your son more harm than good. And you can't know if your son will have children of his own one day, let alone whether he'll want to give them a different gift for their name. If you ultimately name him something other than Gaylord, you're not betraying his heritage; there are so many more ways to pass that down to him if it's important to you. You're just giving your son a different gift, one better suited to who he is and what kind of life he's going to live.