3" barrels are not particularly uncommon on Detective Specials and were a standard length for .22 caliber Cobras and I have a NIB 3" Cobra .32 so it's certainly likely a number of .32 3" Police Positives were made...but how many or few I can't say. I've never seen one. It's probably very uncommon if not outright rare. It may even be a pre-Detective Special piece.
If you look more into it, it would be interesting to know the serial number and when it was made. Maybe someone here would be interested in it if you decide to pass.