Ditto on only seeing one,which,IMO, was ruined by aftermarket engraving and ill fitting pearl stocks. Seller said it had "provenance" to some famous Judge. I also saw one advertised about 15 years ago in Gun List.
Henry Stebbins,in one of his books,"Pistols,A Modern Encyclopedia",1961,mentions seeing some unusually long barreled Police Positives in a store window here in Portland,Maine,when he was a kid,around W.W.One. Henry was not a native,but "a summer complaint"(a summer tourist!). He doesn't state the caliber or actual barrel length,but figures they were specially made for Maine Trappers,who liked the longer barrelled guns(like the H&R Trapper Model .22) as they could use their off hand,with a heavy glove,to hold the barrel and get a perfect head shot on a snared critter,and not put a hole in the pelt!
Never have seen anything over a 6" listed for the P.P. and P.P.S.,in any caliber,regular or target. But I do know that Maine "outdoorsmen" loved the longest barrels. Have 3 7.5" New Services(38/40,44/40 and .45 Colt) and 2 Triple Lock Smiths, one fixed sighted and one a target model,with the very rare 7.5 bbls. Probaly less than 100 made in 7.5.
". All 5 of these came from Maine estate sales.
You probably won't shoot it,and who can blame you,but my little 1972 Cobra .22,with the 3" bbl. is a great little woods companion!
Bud