Back in the 80's and 90's, every dealership, accessory shop sold these visor strips. Lately, they have been scarce.
http://www.ebay.com/itm/motorcycle-motorbike-helmet-visor-decal-sticker-graphic-performance-sun-strip-/201256134470?pt=UK_Motorcycle_Parts&hash=item2edbcce746#ht_11455wt_1104 (http://www.ebay.com/itm/motorcycle-motorbike-helmet-visor-decal-sticker-graphic-performance-sun-strip-/201256134470?pt=UK_Motorcycle_Parts&hash=item2edbcce746#ht_11455wt_1104)
I have one of these on my helmet and they work as advertised.
Fred
Those westerly late afternoon rides can be annoying. I have used black electrical tape. I always keep a roll in my tank bag....a little gummy when you pull it off (adhesive residue on the visor) but some mineral spirits with a clean cloth and you're good to go...
I use these
http://www.aerostich.com/a-to-b-utilities/rider-comfort/visibility/helmet-sunblocker.html (http://www.aerostich.com/a-to-b-utilities/rider-comfort/visibility/helmet-sunblocker.html)
I have used them in Arai and Shoei full face helmets and a HJC modular helmet.
I have used the AeroStitch type sun shade, it works well and is easily swapped from one shield to another. This is the eBay sun blocker listed in the opening post.