score:3
I Google searched some tattoo artists in the Osaka area that have more positive than negative feedback and, although I am not recommending any of them (as I haven't personally used their services), if I were to get one myself I'd probably inquire from the following (random order):
Notes: I myself have no tattoo/irezumi and do not live in Osaka. I live elsewhere in Japan and have been interested in getting one myself. In my experience of checking tattoo shops near where I live, in most cases you have to contact them in advance, tell/show them what you want, verify the prices, etc. Also, I'm not sure about your age but in Japan one has to be over 18 years old to be allowed to have one.