Latin American keyboard on Macbook Air

Nobody in these forums represents Apple sales or any store. To find out if you can buy something in Miami, you have to contact stores there directly yourself. When you order online, they may be able to have it delivered to your local store.

https://www.apple.com/shop/shipping-pickup

In a place like Miami, there is at least the possibility that they could have Spanish-language keyboard MacBook Airs. Most places don't, but there in Miami, it's at least possible.

The best way to find out is to check out Apple online and specifying that you want the Spanish-language keyboard and seeing if any of the local Miami Apple Stores offer availability to "pick up today" in terms of availability. That would clearly indicate they actually have it in stock. You would want to make sure all the other options (RAM, storage) are left to the default values and not customized. There wouldn't be a guarantee, but that would be your best chance.

If for some reason you can't simply check out the store in person with a shopping appointment (like if you were planning on flying into Miami and are only going to be in town for a couple days) you can try calling Apple and have them put you in touch with one of the specific Miami stores so you can talk to them directly.

Short of that, the best way is to simply order it from Apple.com but choose to pick it up at the store...paying very close attention to when the store estimates they would have it (like if you were planning on flying in) and giving yourself a cushion of several business days in case there is a delay.

Also, keep in mind having a physical latin-American layout isn't crucial from the macOS standpoint as it can software-change its layout. Obviously this wouldn't give you the same physical layout, but it's at least something to consider if you had to make do with a US layout.