I have one from my son, and he got it from a guy on the baseball team. But I have not seen them for sale anywhere. Maybe you could try emailing the USMMA baseball coach and see if he can give you direction. Good luck.
I suggest checking out the official USMMA merchandise store or their online shop. They usually have a great selection of team gear, including hats. You can also try reaching out to the baseball team directly or checking with local sports stores in your area.
I first of all take note that the original post is dated August 7th 2020.
I've attached a team hat picture extracted from one of the recent programs. I assume this is what you are after?
Go to Hats, make sure you click on "Show All" at the bottom of the initial page and look through the selections. There might be one that is very similar. I think the difficult part will be getting the flag" letters. The downside is you almost have to explore each design because once you open a specific design, then you are presented with color options and logo options. Then when you close out something you are checking you again have to select "Show All" to continue.
Another thing would be see if someone on Etsy could embroider something similar.