G'day
Old Smithy, and a warm welcome to the ODK Forums.
Urk, that one's not easy, as it's 17"x8 hole, and was originally riveted to the bedplate. Check if yours has been converted to screw fixing, like most other SB models.
I ran a Google search on the SB part number, 591541, and nobody seems to have these bedknives on the shelf any more.
I'd suggest Golf & Bowling Machinery in Melbourne could probably make you one;
http://www.golfandbowlingmachinery.comThis mob have done some very nice custom SB parts for our members, such as grooming reels.
Mod Bonnar Bloke will hopefully chime in here, as he's in Adelaide, and knows the SB scene there very well.