So Singer Porsche offers a open lug nut plated in brass for a race look option. Does anyone know where to source said lug nuts?

Try Otis LA. You can get almost any lug bolt there.

Nope. No brass at all.

Is that any better than the cad or yellow zinc lug nuts?

A guy on pelican makes titanium lug nuts in both open and closed styles. They will hold up better than plated aluminum.

My local speed shop does aluminum AN fitting in brass. Looks cool and cost almost double.

Right near the curb feelers and fuzzy dice, FLAPS

I think it's a nice look.

You can buy open lug nuts in many places.
Get a set and take them to your local plater....perhaps they can do them in brass.