Thingaverse website has some O gauge windows and doors and most of the files you can enlarge or reduce to what scale you want. i have a Ender Pro FDM and get most of my O sale files from there
Now a question for you. I have a file ive tried to print on my printer even though it says better if printed with a resin printer. It didnt work. So ive been hoping to find someone with a resin printer to do it for me. If youd be interested Id pay you for it. Its a very small print. I have a Lionmaster UP Big Boy and theres a mod for the smoke unit funnel id like to try. let me know and i can send you the file.