I sold my Underwater housing for my Canon DSLR a while back but have some bits left.
These fit Canon or Nikon Sea&Sea underwater housings.

Extension ring 40
Extension rinx SX
Optical glass dome port (this cost me some serious coin)
All above, perfect boxed examples, like new

Also a nice 2x8" anodised alu strobe arm

Pm if you are interested.
Cheers