Polychoke is still available for installation. It is about $100 for the choke in the US and requires an import/export license. I would think most gunsmiths would charge about $75 to install one. They require careful fitting perfectly inline with the bore.
I used to install a lot of them 25 years ago. I have customers still using them and quite happy with them. They are not as popular today because of their looks and I haven't installed one in 10 or 15 years...
Most people today are using barrels with interchangable tubes... that seems to be the latest fad.... if you plan on hunting with steel shot and also use lead shot for upland birds, all you need is a fixed choke barrel with an improved cylinder or Skeet II choke and it will work very well with both. Steel shot does not require the tighter constriction that lead does to get a good pattern and distance.