I think its kind of impossible to really come to terms with the exact number of bitcoins that are lost, this is because, when we visit the bitcoin blockchain explorer, and view addresses holding bitcoins, there is nothing indicating addresses holding bitcoin that their respective owners have lost access to, they appear there like every other address normally.
Chainanalysis and other forensic experts might or do come up with some numbers as possible bitcoin that are lost forever, but the truth is that, we can never be sure, since most of the time, those numbers are called from wallet holding bitcoin that haven't had any activity on it for a very long time, that is not an evidence enough that the owner of such wallet have lost access to it.

Well, there is no such place, lost bitcoins are lost, except the user luckily discovers or recovers his or her private key, that is, the key to the wallet containing the bitcoin, anything outside that, there is no other way to get lost bitcoins back, if there was, then the lost bitcoins will not be referred to as lost - in the first place.