You have to be a bit careful when picking a brand. All of the stores mentioned here (Walmart, Trader Joes and Whole Foods) carry museli that is loaded with sugar, which it shouldn’t contain.
They generally also carry have options that aren’t just crunchy candy, but be prepared to read a lot of nutrition labels before you find one.
Yeah, you should be careful when picking a brand, but I don't see muesli with loaded sugar at those places. Are you looking at granola? First off, I haven't seen them in my local stores (outside of Bob's Red Mill[1]). Walmart's website also mentions Familia Swiss Muesli Cereal, says "No added sugar" on the front and the nutritional values don't look far off. Trader Joe's also looks comperatble to Bob's Red Mill[2]
Grains, nuts and dried fruit all contain sugar so muesli will contain some sugar. The key is to not buy muesli with added sugar. Walmart and most of the grocery stores around me sell Bob's Red Mill muesli which doesn't have any added sugar. The grocery store I normally use also sells Alpen brand. I bought some Alpen No Sugar Added muesli there a couple of days ago because it was on sale.
They generally also carry have options that aren’t just crunchy candy, but be prepared to read a lot of nutrition labels before you find one.