There are at least 4 in existence, as there are 4 on outpost, one gifted. This site only has found 2 of them though.

http://www.tf2outpost.com/trade/14123273

Sold with Knifestorm Fuka(~3.4) + Clean Gifted Flops(~1.5 buds) for a V. Max(~11.5)

11.5 - 3.4 - 1.5 = ~6.6 buds

Proof: http://www.tf2outpost.com/trade/13881994

http://www.tf2outpost.com/trade/14019185

Sold for Ghosts Beak(~6.3 buds)

Proof: http://backpack.tf/id/76561198081174617?time=1378018800 -> http://backpack.tf/id/76561198081174617?time=1378105200

http://www.tf2outpost.com/trade/13964529

Possibly involved in some complicated trade for a duped Sparkle Luger, not sure what it sold for

http://www.tf2outpost.com/trade/13862771

Sold for 6 buds pure

Proof: http://backpack.tf/id/76561198028274698?time=1377586800 -> http://backpack.tf/id/76561198028274698?time=1377759600

http://www.tf2outpost.com/trade/14256563

Not sure what it sold for, found 72 keys from the next owner, but he bought both DP brainiacs together, so that clearly is not correct.

http://www.tf2outpost.com/trade/12945513

Sold for duped Moon Fez(~10.6 normally, outdated, and outlier)