Last time, I had 3 belts to make for clients. So I ordered these wonderful straps from a french supplier that sells colours straps pre-cut the sizes I need.
They also have a collection of buckles for belt so I ordered some of them as well as replenish my stock of D-ring belt keeper.
I published a guid for making belts if you ever need tools, leathers, and some pieces of advice.
https://shop.crofte.fr/create-leather-belt-beginner-guide