You're right. Inventory usually does a run of plain Ebbets field flannels for the winter, which have adjustable straps (seems they might only have twills now, though). I've seen other companies that run plain ebbets as well but can't remember off the top of my head.
Fair ends has some flannel baseball and camp hats, which are adjustable (but not leather). I'd be wary of them though; I just received their waxed olive baseball hat and the strap became detached immediately. Waiting to hear back about a potential exchange, but wondering if this run could have been bad.