EG ones are miles off, I’ve checked - even trimming them helps in no way!
The only Prelude Spoon style mirrors I am aware of with the flat baseplates are made by Vision (or were), but there are only a handful of them around the world, never seen any in the UK.
As Nath says, people have made do with Integra baseplates, even Dino’s old white lude had genuine carbon Spoon ones from an Integra. There’s a set on ebay right now – the real deal but at £299 is somewhat steep!
They never seem to come up for sale in the UK, look on ebay.com and search worldwide from the states and there’s loads of cheap copies with the baseplates, the shipping bumps the cost up between £60-100ish.
And for the love of god, don’t order any from the UK. There is a brand (can’t remember the name) that lists DC2 Integras but having tried two different distributors they’re the same as the EG ones I have in the garage. They also have the triangle recess for the usual M3 / DTM / etc mirrors, like this:
You could make your own, I made some a while back with some ABS plastic, but the mirror area recesses in quite a bit so a flat piece of whatever does look a little odd. By all means have a go though.
Hope that helps. Cheers,
Rob
You know he's on about the triangles that the door mirrors are mounted to right, not universal mirror glass 
...im off to bed.
