This hat is 1 of 1 to my knowledge. I have been recording all strontium sales on Outpost and Backpack classified for about a year and this is the only recorded one I have found.

I bought this for 35 keys pure: http://imgur.com/a/kjkcA

The previous owner has had this hat for a long time. February is the first time he put it up for sale to my knowledge: http://www.tf2outpost.com/trade/27850757

I am a collector of Strontium Stove Pipes and I will not sell this anytime soon.