The GP-100 .44 Specials 3" stainless models are still listed in the Ruger 2019 catalog, so shooters who want one can buy one new. I have never seen any new or used models for sale in the area gun shops and just a few new or used in our own classifieds. It might be considered by a few to be just one of Ruger's oddball revolvers but to me it is a fun to handy trail and home defense double action revolver. And one that is fun to shoot too.
Ruger 2019 Catalog:
https://ruger-docs.s3.amazonaws.com/Ruger_Firearms.pdf