We don't always have keys in stock. We only get more in stock when other users sell keys to us. This is heavily dependant on the current market situation and key prices.
In key banking we only accept normal Mann Co supply crate keys. This means that we do not accept other keys like : EoTL keys, nice keys, naughty keys, summer keys, etc.. We also do not accept/buy keys that were event keys and turned into normal keys.
However, in item banking we accept some of the alternative keys.