I've been doing some research on air coolers for this case over the last week or so, and there are very few options in this category that I personally would find myself happy with as far as noise and thermal performance is concerned... As you said, the C7 and C7 cu are both completely gone from the market, and Black Ridge seems to have compatibility issues with a lot of motherboards, and also has some availability issues depending on your region. The suggestion for the Silverstone AR11 with a Noctua NF-A9x14 from
@Solo seems to be a front runner for sure, but since you're using AM4, I think the L9a will beat it with a 120mm slim fan attached (replacing the 92mm it comes with). It bums me out that the L9i is outperformed by it's AM4 sister cooler (I'm on the Z390 platform), but that works out in your favor. I'll continue researching, but I feel like if there are better options, they will likely come from frankensteining passive coolers with oddball fan setups. I hope better options arise, though... as I'm tired of the pump noise from my H60, and would prefer a full length GPU haha.