Did you find one in the end? I've decided to necro-bump your thread as I found it while looking for info on a new pickguard for my 1981 Blazer, so figure someone else might find it looking for the same...
Here's a tracing of my pickguard - for scale, the lined paper it's traced on to is A3 sized (420mm x 297mm or 16.5in x 11.7in)
It looks like my bass has a different bridge than yours... I don't know if there are slight variations in bridge/body sizings, but for comparison here's my bass:
If anyone is aware of other sources for a pickguard, other than Dalkowski's suggestion above, then feel free to chime in... I'm always happy to look at more options