Valleriani

I was writing something out and someone said that 'You can win special armor!' as a line is incorrect. They stated that it should have an article, aka 'You can win a special armor!' To me, both in this case are correct. I know you can't 'win special weapon', and the article would be removed only when it's a plural in this case, aka 'win a special weapon'/'win special weapons'. If the above 'win special armor' is correct, why is that? Is there a rule or logic to why that works in this case and sounds correct?