Only over 1 page of unpainted ones on Outpost, some having collector's levels and some selling for 2 keys (good luck).

Sellers at 1.1 keys:

http://www.tf2outpost.com/trade/24126048 2 weeks old.

http://www.tf2outpost.com/trade/23397493 1 month old.

Sellers at 1.2 keys:

http://www.tf2outpost.com/trade/24314833 1 day old.

http://www.tf2outpost.com/trade/24041976 2 weeks old.

http://www.tf2outpost.com/trade/23987484 3 weeks old.

Unsolds at "backpack.tf price":

http://www.tf2outpost.com/trade/24218978 1 week old.

http://www.tf2outpost.com/trade/22607594 3 months old.

Classifieds at time of posting: http://backpack.tf/classifieds/?item=Physician%27s%20Procedure%20Mask&quality=3&tradable=1&craftable=1

1 for 1.1 keys.

4 for 1.2 keys. (one of them is painted black and renamed, but gifted)

2 for 1.3 keys.

1 for 1.4 keys. (painted pink)

1 for 1.5 keys.

Everything else is over 2 keys.

Any additional proof, counter proof and constructive feedback is appreciated.