Cigarette lighters seem to go for good money every time they hit eBay. Seems all you'd really need to do would be to create the proper knob and thick chrome washer - the rest of it is really just a standard lighter. These were also used on Jaguars and a few other British luxury cars, so you'd have an expanded marketplace for such an item.
Ignition lights are a similarly high-priced eBay item - by creating the brass/chrome stamping you could potentially then make the full set (ign/indicator/beams/overdrive).
Fog/driving light brackets are also NLA, I think, and would be rather simple to make.
An original factory boot-rack, but made up in stainless to make it permanent.
New stamped-alloy triangles to fit the door openings (to match the sill plates).
Rubber mat sets to match the original floor material.
Rubber door furflex caps. (The little cap that sits on top of the furflex at the top of the windshield and finishes it off - I have an original for use as a pattern).
Rubber heater drain boot (not just the duckbill - those are available - but the more complicated rubber item under the heater core).
Hard-top hold-down escutcheons (that fit into the boot hinges) for the later series hard-tops - there are very few left that are not pitted.
Passenger-side false-floor panel. (I have an original for a pattern).
Plastic handbrake base covers.
Original choke cable asssembly (you just need to make a proper original knob and affix it to an off-the-shelf exisiting cable).
Hood-cover support straps for the Series V cars (the strap that is anchored behind the rear passenger bulkhead and has a hook that fits in the back rail and a fastener that connects to and supports the convertible top boot when the hard-top is on or the convertible top is up). (I have an original one for a pattern, but as with all of them the rubber strap has lost its elasticity).
A proper Class I trailer tow-bar that fits the Sunbeam range might be something of value, though clearly not an original fitment.
Timing covers that are retro-fitted for a neoprene lip seal - again, not original, but could sell well and fit the entire range.
The optional rear seat cushions are NLA - even Martha Wheat does not make them, I don't think - so they might be a good seller. (I have an original set in excellent condition if you need a pattern.)