Hello Viking,
Thank you for your answer.
However that is exactly the problem i have : the apps disappeared from my AppStore account, even though i previously had them on my computer. And my account + clean install were all made with the same Apple ID.
As you can see below, i still have GarageBand, iPhoto and iMovie which were all part of the suite, even though i deleted them from my computer :

I spent H.O.U.R.S... on the phone with the Apple Support, level 1 and level 2, and it seems they can't do a thing about the problem on my account.
As i'm on a outdated computer and system, some tech juste answered they can't help at all, some tried to help me and actually succeeded to make Pages come back on my account. However i'm still missing Numbers and Keynote.
The last tech level 2 for iCloud account i had yesterday, 2 hours on the phone, finally told me he has no idea how the other tech succeeded in bringing back Pages and can't help me any further as even the Apple Support doesn't have the install package of the apps.
And what is also annoying is that on the download page of the Apple Support you can have the older OS, whereas there isn't any older version of their apps that go with the OS...
So he advised me to come on the Community to find it, and if i installed the app with the official Apple install package, this will bring back the app on my account.
So if you have any idea how, or where i can get those install...
Thank you for your help,
Sébastien