Al,

I was finally able to track down a plate on ebay.au, but it is missing the screws to mount it with and to fasten the sight to the plate. When I inquired about the screws, I got this answer:

Bill,
I don't have any spare screws. The No.4 rifle needs two screws for attachment of the plate, one is the safety spring screw that is on your rifle, the safety spring is removed for fitting, the rest of the safety is left in place and the safety spindle acts as a locator for the plate. The second bottom screw is an extended rear trigger guard screw it is 4BA in size. Some people grind down the thickness of the plate at the bottom to allow the original to fit but it doesn't leave much meat on the plate, it's better to get the correct length which is 1/8" longer than the original. Specialty bolt and screw places sell these and a mate of mine bought some in the USA but can't remember where from.The third hole in the plate is for adapting the plate to use on an SMLE Rifle No.1, the tits on the back of the plate are ground off for this. Whichever rifle, these central plates need wood to be removed from the fore-end to fit. Target shooters usually just chisel out clearance but it can be done neatly and smoothed into the line of the fore-end.
The screw that attaches the sight to the plate is 2BA size, most people here use slot head or hex head because the wing bolt looks good but breaks easily if over tightened.
Rob

The expression "4BA" and "2BA" mean nothing to me. Could you translate please and perhaps point me toward a source?

Thanks,

Bill