I happened to come across a whole bunch of these light blue belts that you can open in three places. First there's the ordinary belt buckle closure, then there are also the two golden coloured clasps that can be opened. If you wish for a shorter belt you could just cut it by one of the clasps and close it back on.

The belts are mint deadstock and in very good condition. If you want more than one you just give the number by the checkout. I've used 3 or 4 at once myself, over a 40s dress, it was very fancy!
Length: 83 cm is tops, and then you can always cut it as short as you want to.
Width: 1½ cm