If by "it exists", you mean that there are dialects in which those are the pronunciations of "piano tuner" and "tuna sandwich" then I'd like to know more, but I

If by "it exists", you mean that there are dialects in which those are the pronunciations of "piano tuner" and "tuna sandwich" then I'd like to know more, but I've met many people who speak dialects without the so-called intrusive R and don't understand how it works (but think they do). With intrusive R you get "tuner and mayo" but not "tuner sandwich".