Hi Amy!
I'm also very particular about the kinds of hats I wear (because of my bald head!).
What I've noticed is that the merchandise available often looks quite different from one visit to the next, even if it's only been a few months. I love to go shopping at Walt Disney World (let's just keep that our little secret), so I really like the fact that each visit holds a whole host of new treasures to find. So, while you may have struck out on finding a lot of fitted hats on your last visit, you may find a whole new crop of options on your next visit.
The other thing to keep in mind is that the Disney Merchandising team does a great job of spreading out their inventory across the theme parks, resorts, and in the Downtown Disney area. As such, you may find a souvenir in one shop that may not appear in any of the other shops on property. You can always ask a cast member to help you locate an item even if they're not carrying it in their particular shop.
Other options might be to check
The Disney Store Online for their Disney Parks Products or to call the Disney Parks Merchandise Guest Services line at: (877) 560-6477.
As for the firefighter-themed gifts at the Firehouse in the Magic Kingdom's Town Square, unfortunately you're right. However, it may be worth a shot to check out the Disney Design-A-Tee shirt shop in the Downtown Disney Marketplace. You can create customized t-shirts via kiosks and have them printed while you wait. The artwork to choose from is regularly updated, so I can't say for certain what they'll have during your next visit. However, I've created my own shirts before and it's definitely a cool souvenir!
I hope that helps a little. If you have any other questions, please feel free to send them my way and I'll be happy to help in any way that I can!
Best regards,
Derek