For finished stuff you could also look at reddit, since there are general subreddits like "mapmaking" and some that are specific to software used for creation like "Wonderdraft" and "Dungeondraft". You could also look through sites where art is posted like DeviantArt to see what you can find. I think the reason there aren't a lot of premade city and town maps on the marketplace is that it is very hard to come up with something fairly universal. Even for a "fantasy" setting, you have the variations based on the scale/availability of magic, scale/availability of tech and mechanical innovation, and even the variety of species involved in the world that may influence how communities would look. At one point, I thought about trying my hand at some premade communities for the Marketplace, but when I really started thinking about it, I realized that I could really only make ones that I was sure would work in the types of world in which I run my games. There is really no way to flesh them out with shops, districts, and npcs without limiting their usability by others. That is the bane and promise of tabletop gaming. You can make the world uniquely your own, but it is uniquely your own and not necessarily directly compatible with what other people are doing.