I think it was Dover Press published several books of HO buildings a number of years ago; one was a commercial downtown area, which included a movie house, and about a half dozen stores and a passenger station. They also had a book of Victorian houses, and one or two others. I tried reducing to 54% and printing one on an ink jet; the results were pretty good, although some of the pieces got pretty small to handle. The biggest problem was getting the printer to match the screen colours, but that can be managed. Once assembled the buildings looked pretty good, especially for background stuff.
I also considered using Grandt line windows and doors to replace the printed ones, and found myself then considering Evergreen styrene products for shingles, and then clapboard siding, and then brick.....and, aw, what the heck, I tried building my own stuff from scratch. So I never finished the card stock buildings. But, you know, it's a great way to get started!
I think these publications are still available, although it might take some searching. Probably Amazon.com. Hope this helps.
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Harpo