Maybe look at purses or wallets or shoulder bags. The shapes of intersections and overpasses and the railings on bridges. Public gardens and fountains. Street signs and traffic lights. The texture of concrete in different forms and uses. Wall coverings (paper or cloth; marble; paint; brick; tile…). Landscaping. Doorknobs and handles. Stairways and elevators. Waiting areas for the bus or train. Billboards and marquees. Clocks and watches. Hair clips. Key chains. Drinking glasses.
Even when more schools had art programs, they were limited. Unschoolers are not limited in their exposure to art in the vast everyday world.
Although it shouldn't be the starting or ending place, don't forget that the real world includes books and videos. There are museum sites online, too, with images of art you can zoom in on.
photo by Sandra Dodd