OP asked for 125B, but for those looking for 1590BB, Amplified Parts has them in their store, Reverb, and eBay.
https://www.amplifiedparts.com/products/chassis-box-1590bb-diecast-471-x-370-x-118
https://reverb.com/item/2976068-chassis-box-1590bb-diecast-4-71-x-3-70-x-1-18-color-brown...