TheBigLLS: ... Is there a site that also offers some kind discounts but for a games that can be tied to GOG account?
Tieing games exclusively to a GOG account is like Steam exclusives. Sounds good to the distributor in question but bad to everyone else.
So far GOG only distributed games and did not possess games. So there was no reason to sell them indirectly over another store when you can sell them directly here. That would be just too much levels of indirection.
Now with GOG actually starting to become publisher their games may also be sold somewhere else (on Steam for example). But that's not what you wanted.
You wanted for example retail games that have a GOG code inside (and nothing else). Well while this is possible I doubt it makes much sense (although for Steam it seems to make sense) because well, you just have two sellers in a row then and both want cuts, but the product doesn't get better.
So, except maybe for marketing purposes, this does not make much sense.
Also people wanting to support GOG should buy their games directly from here.