I can't create a giveaway for Blockstorm

Maybe it was given for free on indiegale or something else ?

Correct. :)

it was free, u cant create GAs for free games, thats all

Thanks ;)

you can check this: https://www.steamgifts.com/discussion/dsq6C/discussions-that-should-never-go-away-aka-sg-bookmarks
and this inside: https://www.steamgifts.com/discussion/pJRbR/can-we-have-a-list-of-games-that-cannot-be-created-as-giveaway-unofficial-list-inside

It must have been given away for free. You can always check out the trade forums or sign up or try out this site barter.vg