The original clips seem to have been manufactured by a company called TRW and they produce a very similar two piece clip, these are supplied by a retailer called JetPress and their reference number for the clip is TPF071, here's a link to the relevant page:
https://www.jetpress.com/component-and- ... utton-type
The alternative clip isn't identical, the yellow fir tree part of the clip is different in having only one pair of barbs (the original has two) but otherwise I think it's a good match.
I've asked them for a sample so that I can compare it against the original clips I have,
Steve