I just put a piece of wood at an incline at the bottom of my goal. After I made it, it'd bounce on that back in my general direction. Otherwise I just rebounded myself. I always played conditioning games. Start by shooting a long jumper, then make, if miss rebound and shoot with off-hand, if miss, rebound and shoot with normal hand, if miss then by this time I should be close enough to do a layup with the off-hand, then rebound and start over.
It's difficult playing by yourself, but you can improve with focus. Don't worry about the number of shots you're getting up, worry about the quality of those shots.
You should be able to shoot solidly (10-20 shots a minute depending on shot distance/type) for at least 20-25 minutes while focusing on good form and rebounding for yourself and not getting too tired. If you can't do it that long than push yourself until you can for conditioning-sake.
I require my kids I coach to be able to do it for 25 minutes straight and they have to continue to shoot at least at a rate of 10spm (shots per minute) in middle school, and 12spm in high school. All while focusing on continuing their form and jump height on jump shots. Also, the rebound cannot bounce 3x before they grab it and shoot it again. Every 3rd shot has to be from at least 15 feet away so they're not all just shooting 5 foot jump shots. They have to do this 4x/week as part of their summer conditioning program. They work up in increments of course, start with 10 minutes, add 5 minutes every week-ish until goal is reached. I had one kid who had amazing stamina (best defender I ever coached...could hound the ball all game long on point guards) that could run this drill for almost an hour straight with good form.
Always remember when practicing any type of basketball-related skill, quality over quantity. Shooting 1000 jumpers a day is great, but if you're just runnin' around shooting haphazardly and not practicing the shots you'll take during games then what good does it do you? Shoot free throws, shoot set shots, shoot runners, shoot post-up moves, shoot pull-up moves, shoot off the dribble, shoot off rebounds, shoot how you play and shoot with a purpose.
Again, for rebounding help, I just got a big 1ftx4ft piece of plywood, leaned it up against the base of my goal and the ball would bounce back when it hits it. It really only worked on makes or short shots, but the more I made, the more the ball came back, the more I got to shoot. (Just don't shoot layups with it around the base of the goal, that's a broken ankle my friends).
Hope that helps.
