Where can you buy hip belt buckles?

Questoutfitters has some 2 inches wide but I don’t know if that’s any larger than what you already have. https://www.questoutfitters.com/Fasteners_Side_Release.htm#SIDE_RELEASE_BUCKLES

I would look at the cobra style belt buckles, they come in a variety of sizes.   I find that they last longer and in an emergency, a real one will allow you to release it under load

There are different variations.  This one will allow you to adjust it from both sides of the buckle.   They also make a non adjustable style if you need to see it in (your pack may adjust the straps from the pack, not the buckle).

AUSTRIALPIN Cobra Buckle 2″ Dual Adjustable No-Sew https://www.amazon.com/dp/B06XKPPGNV/ref=cm_sw_r_cp_api_i_Y9539J6WGZ4ZW6D7TMBH

Take a look at strapworks.com in Eugene. A wide variety of cordage and hardware. Generally larger than the tiny ultralight stuff that Dutchware sells, so they might have what you’re looking for.

Rockywoods have them