Blk Mirror housings keep turning grey

[Al S]

How can I keep my black mirror housings (plastic) from turning grey? I used
to use a product called "Black Chrome" and it lasted a long time. I can't
remember who made it and I don't see it in my local auto part stores.

I tried "Mothers" Back-to-black, but it doesn't hold up in this Hawaiian
climate.

Anyone know if Black Chrome is still produced or somehthing that will keep
my mirror housings black?

TIA

Al Streicher
Oahu, Hawaii
'90 80 Non-Q  Blk