Porsche still sells them new in slightly convex for passenger side, & flat glass for driver side - which you'll need to flip upside down to use on RHD's bass-ackwards sides (compared to Euro/USA/Canada) - i.e.: convex on left & flat on right. Note that there is only a slightly convex surface, so you can't tell it is as easily, as on modern car mirrors.
AFAIK Porsche also still sells the gaskets & screws. 914Rubber may also sell one or both, & GoWesty.com sells SS screws for the Vanagon side mirrors which are the same size/type as for 914 (& Bus/Splitty IIRC), or you can probably find SS screws locally.
If those are too pricey, then you can simply use 2 of the standard driver side ones at both sides (R-side flipped vertically to work). Just get the best condition within your budget if used, from on here & the other usual used parts sources online. You also have a few other 914ers down there in OZ who may be able to come thru with an extra one locally.
BTW - the R-side door already has the nuts welded into the underside of the door skins on all 914 doors, so all you'll have to do is locate them & drill down from the top, & rust treat after drilling with Wurth, Eastwood or some other zinc rich primer.
Should be a simple task in the land of OZ!
Cheers Mate!
Tom
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