@Oldbloodblaise
Unfortunately, Red Alert 2 does not exist on Origin as separate product, so unlike other games, it can't be redeemed from a key. Also, the Origin version comes bundled with the Yuri's Revenge expansion, and as far as I know Origin has no support for giving multiple keys to redeem one game.
The game was given away a while ago on Origin's "On The House" feature though, and that RA2+YR was in fact the one from The Ultimate Collection (it has the TUC logo in the corner of the icon on the Origin games list), proving that it's possible in the system to have only one game of the whole collection.
So, you never know, maybe if you contact an Advisor via EA Help and get a live chat session and can prove you got the original game(s), maybe they'll give you a digital copy? I honestly have no idea about their policies surrounding that, but this answer from an EA support team member on a similar question does seem hopeful, so you might get lucky.