I modified an existing pouch for my DAN SMB. It might work with what you want to carry in it. It doesn't have any internal pockets for the small stuff like a mirror or whistle, but you might be able to tie those to your SMB.
The pouch is from Deep Outdoors which I got from Scuba.com for $5.95.
Deep Outdoors LDS-Single Accessory Cuff 03040 with reviews at scuba.com
I had two knife grommet attachment points already on my BCD (Aeris Atmos LX) and drilled holes through the stiff backing of the pouch to match the grommets.
I then ran a 1/2 inch wide zip tie through the holes and grommets and cinched it tight.
I added some fastex buckles to make it easier to open and close.
I've since switched to a BP/W setup, but I still use this accessory cuff as it slides on the waist strap perfectly.