If I follow what you are saying, I'm guessing you want a similar cover to that illustrated in Lucas Workshop Instructions Volume 2 Jan 1953 L-2 Part A in Fig 2 on page 2?
Doesn't state what version of the E3 that's on though and the workshop instructions don't give part numbers.
200496 doesn't figure in the comprehensive Lucas parts lists up from 1936 - 1957. Maybe it's in another list somewhere but a search hasn't thrown it up for me.
Part 200495 does figure though, and is a grommet.
E3Ls are listed in the Parts Lists (Dynamo and Supercession Chart, Section E, page 5) as having 200826, which has a triangular raised bit of moulding similar to the replica, or 200902 or 918, which are the metal covers. There are various earlier types of covers illustrated in various places in the Lucas literature, but probably not relevant to any E3L.
It's possible to spend literally hours trawling through these lists. They are available in the Service Literature section of the forum (I think) if you want to have a poke around, or Google might be your friend. Whether there are any other new replica covers available, beyond what you show, I dunno, but they probably come up in various states of (dis)repair at autojumbles.
