Long shot stuff..
but I still want to get a set of extractors for the XJR and my mechanic is currently fitting a nice set of V12 extractors to a road-race Xjs . They were made by V&A Spiteri in Melbourne
They don't list X300 extractors on their website but I have emailed them to ask (awaiting reply)

One option would be for a Melbourne X300 owner to let them use their car as a template, then build a jig and turn a few out.
I am on the wrong side of the Tasman sea for this exercise!

Anyone interested?