I think Redline Components is your best source.
https://redlinecomponents.co.uk/
I would call Chris Mintoft there.
HOWEVER,
MV8s suggestion is good, to have one made. It's a very simple piece to fab up, and could be made with additional strength. The A frame one of the things I would agree isn't worth the expense of a factory made part. These aren't Concours D'elegance cars. It won't ever be scrutinized for originality.
Do plan on continuing using the original soft rubber bushes, not the hard neoprene.