Rear wheel assemblies

Hello, I’m a beginner to the mini bike space and have challenged myself to create a bike fully from scratch to cruise around the neighborhood. I want to emphasize that I will not thrash the bike or take it off road. I have a frame, front wheel, and engine the only thing I’m missing and not really willing to build or find myself is the rear axle, rear wheel and tire, brakes, and sprocket. I’m not really sure where to find it, but do these exist fully assembled and ready to plug in? Can I find them used from something else? If any questions I can answer for the best possible option thank youuuuu