I saw your pm but can't ( yet ) reply to it
the ones you describe are indeed the ones I was thinking of. From your description of the colour I'd guess they are quite old and could be seized onto the helmets, or the mounting screws be seized inside. They are best left as they are, but thanks anyway.
the brown resin MSA helmets are still in use in the US and you sometimes get them issued in the offshore industry, the full-brim hats are still popular there and hard to obtain. They are also popular with welding personnel because the smooth shell and 'waisted' peak on the cap-style ones means they are good for mounting face shields etc.
plus, the MSA hats actually fit properly and have a cold-weather hood which fits the lining, you'd think that would be more common than it is!
anyway I have acquired a couple of them from a recent job, and since I do sometimes wear a caplamp for tank entries and so forth, I thought it would be handy - and one would make a nice wall-hanger.
I've discovered an American caving shop which can supply them, so I have ordered a couple.
''the stopes soared beyond the range of our caplamps' - David Bick...... How times change .... oh, I don't know, I've still got a lamp like that.