I was actually wondering if you had it scanned (presumably there is now only one place in Vienna that could handle this, and it is prohibitively expensive) - or if you photographed it yourself. I can imagine how difficult it is with a camera, regarding proper lighting, but also the size, since you would want to be able to make reproductions to original size. Of course you do have some of the best equipment. From a technical point of view, in order to get a large file of it, did you take it in sections and stitch it in Photoshop?
Your size would fit the scanning table here at Gerald Schedy - but the prices are quite something: https://schedy.at/ - he doesn't come quite out (you have to contact for a quote), but a friend of mine said he was quoted years ago € 280.- for a painting by far not as large as yours.
Myself, some years ago I had a few pieces scanned by Digital Laut, but I hear they don't do it anymore. There still is this page on the net, but no link to it from the official site anymore - https://www.digitallaut.at/de/produktion/large-scan/ - I tried to contact Horst Kaiser (GF) but didn't get an answer. In 2017 I had a few works done there, and the prices then were between € 50.- and 80.-. In times past, this company was doing work for Ernst Fuchs, and more recently Joshi Bramer.