example, I want to find a trade where the seller wants to trade his CS:GO keys for my TF2 keys. I spent a couple of minutes trying to figure this out but couldn't find a way to successfully use the search system. Has this feature been removed from the site?

Method 1: Search for the type of CS:GO keys you want (e.g. Falchion), then you should be able to reach the corresponding market page: https://dispenser.tf/market/12832/

If there are already ask orders, you can meet them with a bid order and buy the items instantly. If not, you can create a bid order and wait for others to fill it.

Method 2: Deposit your TF2 keys here: https://dispenser.tf/view_credit_general/ , then withdraw CS:GO keys out from the same page. You should look at the rate and see if the price suits you before you do that.