I still have the box Gordon shipped his spare parts box in. As you can see he numbered each box and insert but unfortunately not like an artist does a limited edition print such as 678/1000. So it is anyone's guess but I think there would have been at least 200 and likely no more than 500. Additionally I wonder if he shipped them sequentially? If he did and those remaining in his estate end at 300 (just picked that number arbitrarily) then we would have our number. Maybe?
I need to check the number that was added to my GH spare parts container next time I am in England, as I only bought it earlier this year, if they were sold sequential, it'll be interesting to confirm what number it is.