How to get free Steam Keys without using Humble Bundle

You can also buy bundles and single keys on Fanatical.

i am not sure if i understand the question correctly.... you get free steam keys from humble bundle from time to time (promotion so you don't need to pay something there, you only need an account for it). You can give them away here but you will get no cv for it.

But if you are looking for other sites where you can buy steam keys to give away there are a couple ones out there (fanatical, greenmangaming, indiegala, and so on)

Like Patzl pointed out, free keys won't give any cv, it does make sense doesn't it? I mean, you got it for free while others pay for their keys so it's only fair you don't get any rewards for it.
If you want to buy keys, you have multiple websites, not sure why you only point at Humble Monthly while Humble alone also has way cheaper bundles and then there is also Fanatical and IndieGala if you are looking for some cheap keys.

If you want to get games for the sole reason of leveling up, Indiegala / Fanatical bundles have (likely) the best money-to-CV ratio (though currently it's the HB Humongous Bundle afaik, you get ~$10 CV for giving away full tier 1 which costs $1).
Also Humblebundle, Fanatical and Indiegala are official , legit stores, their keys should work, and these keys are a lot easier to handle than Steam's gifting system.

Level-wise:
level 1 is "mandatory", you'll see quite a lot more giveaways compared to level 0,. If you give away a single game that worth CV - you're already level 1.
Level 2 is useful IMO, you'll need $25 worth of giveaways for that. (Real CV, bundled game worth 1/8, as stated in FAQ. You find info about levels in the FAQ as well
Level 3, maybe 4 is more than enough if you just want to win games and don't buy bundles for yourself. They are at $50 and $100, respectively.