The forum has reviewed upside down holsters more than once. The original was Berns-Martin's "Lightin" (no 'g'), famous not least for being intended as James Bond's shoulder holster -- for the then-new Centennial -- and being specified for the Walter PPK that was being discussed with the author as being a European baddies gun.
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The most knowledgeable about the B-M's peculiar history is turnerriver. In general, though, the market began there and was supplanted by the elastic form, apparently created by Wally Wolfram by the early 1960s. John Bianchi and Neale Perkins both copied it, Bucheimer and everyone else jumped in -- and then the pistols started falling out. No maker except John realised why and gave them up.
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The Bianchi elastic version was called the #9. Avoid these, whether new or a half-century old as they are now. It was replaced by the #9R, the letter to distinguish it from the old. During development it was code-named 'baby 27' as it was derived from the new police duty holster with wire-form spring and internal cylinder pockets.
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Still fell out, so an equivalent to the B-M internal spacer at the muzzle was added (one person on this forum actually owns one of the originals without it) -- and the guns stopped falling out even under a harsh test we developed to sort the good from the bad.
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The best of them, if I do say so myself, then, was the #9R-1 and -2. I 'think' the difference in the numbers refers to a change in the spring itself; unsure because it was a long bloody time ago. Both, though, are visually distinguishable from the #9R and the #9. The early #9R is shown in crazyphil's post, and the -1 or -2 is shown in at least one other here.
Leftie harness: in a jam, leave the setup assembled for right hand and just -- put it on backwards; that is, put your right arm through the leather harness yoke and the left arm through the elastic cross strap. Work exactly like a left hand harness because that's all a leftie is: the leather was turned over on the clicker machine, and the same die is used to punch it out.
The holster itself is literally the same for left and right; and the belt slots are even rh/lh. We were quite obsessed with ambidextrous holsters because (1) JB is left handed and (2) it reduced stocking units (called 'skus').
Looking up the OP's pistol tells me it is a Centennial in size; i.e., it still has a five shot cylinder. The muzzle of the revolver is a bit larger, so one might even prefer the Detective Special version which was always moulded 'round the 'new' (how old am I) Dick Special with the longer, bulkier barrel and ejector rod shroud.
Bianchi doesn't make it now, so one would find it on eBay, for example. Things to watch out for: you want the 'lips' of the holster closure to be aligned; when the spring goes 'wonky' inside the holster shifts out of alignment; and you want assurance that the spring itself hasn't already snapped at the muzzle end; and you want assurance that a finger snapped through the opening still makes a loud 'pop' to tell you that the earlier owners haven't 'sprung' it trying to get a faster draw.
Alternatively, there is ONE elastic shoulder holster that actually works: the Bianchi 209 (in soft harness leather and 208 (same holster but constructed from thin saddle leather). The former is far more commonly found on auction sites.
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Whew, I just wrote an encyclopaedia entry. Mit pics.