Yes - loads of places, they are the same thread as fairing screws, so take your pick (Halfords do a selection of colours) of bike shops/eBay etc.
Don't panic about using alloy screws, you can fall off as much as you like and the screen doesn't break. I don't know why Yamaha use plastic ones that break if you look funny at them. I changed to black anodised alloy years ago.
here for instance ->
http://www.ebay.co.uk/itm/KEITI-Wind...item4aa8fae014
http://www.ebay.co.uk/itm/KEITI-Wind...item4aa8fae2eb
http://www.ebay.co.uk/itm/KEITI-Wind...item4aa8fae703
http://www.ebay.co.uk/itm/Rubber-Fai...item20bc3fb432
Oxford do sets too.