Buckle for 2 inch Webbing Straps, Side Release Buckles 2 Set + 4PCS Tri-glide Slide Plastic Clip Fit 2"(50mm) Nylon Strap Webbings Belt Backpack Replacement Dual Adjustable No Sewing Heavy Duty Black

I would absolutely pursue a replacement from Patagonia. You won’t find one in their web pages and need to contact customer service. If not, there are all kinds of backpack hip belts available. All the ultralight manufacturers sell separate hip belts. It really depends on the dimensions of the tunnel the belt runs through. You could buy 2” webbing and a buckle to make a basic unpadded belt. Make sure the buckle has adjusters on both sides: https://www.amazon.com/dp/B08S2WZ7VD