Can't Find Games on Search function when creating a new giveaway

That is most likely because the game was given away for free at some point. If a game has been free at any point, it will not longer be selectable as a giveaway on steamgifts.

Hello Vechhio!

The game mentioned has been given away en masse at some point and therefore has been removed from the giveaway list. This is to prevent abuse of the current CV system since we are currently unable to distinguish between copies acquired via such promotions and those purchased.

For more information on such promotions, I would recommend following the Deals section of the forums that you can find here: https://www.steamgifts.com/discussions/deals

There is also a subreddit which lists promotions: /r/FreeGamesOnSteam/

I hope I have answered your question today and I wish you a great week! :D

Oh, I see. I got it from a pack of random steam keys that I bought a few days ago :p . Thanks for the help.