Lea, You can go to https://www.kelloggs.com and get the rice krispie recipe right online. As for making them with other cereals I do it all the time. Cheerio bars (using plain cheerio’s instead of rice cereal) was a big hit. Also I have used that cheap wheat puff cereal instead of the rice too. Btw, the “newest” version on the cereal bar that I have noticed lately cracks me up. Muffin bars.
Now what is the difference between a regular muffin and one that is in a bar shape? Except that people are buying it waaaay overpriced and from a box? If I wanted muffin bars I would put the batter in a square pan, cut when cooled into bar shapes and put in snack size baggies. Then I would about the same amount as in those boxes.