I'm looking for a Cd-keys suppliers for Steam/Origin

greenmangaming.com ?

I don't even...

This is a forum for ordinary steam users, not shop/store owners.

I think you would be WAY better off contacting GMG or an equivalent directly or
trying to find answers using google, rather than hope someone else here will find the information
for you online.

If you have to ask here it's not a good idea to think about opening your own key business.
Get a real job instead.

"I'll be lazy and make money off of other people's talent for a living"

one thing, if you are not the original and authorized supplier directly from game publisher or sometimes the developers, how could you get the lower cost and price than your supplier since when you are using one or more suppliers as a middle man and they could also have their store at the same time. From what I understand, most of legit online cd key stores have their own supply channel like they directly contact the publishers' branch at their locations and buy retail or digital copies from publishers at a large number for instance maybe over 100 copies of each game. So they can get about $15-20 discount for each copy.
and so it is better to contact publishers or find your own way to get supplies than using some suppliers as middle man while they are selling same things at lower price.

Well, this can be considered trading, so you would be better of on SteamTrades.com.