The supermarket brands are often just other brands with different labels. I worked in a paper products factory one summer and most of the time they just changed the patterns and the wrappers for paper towels - (sometimes the paper would change). My flatmate worked in a canned goods factory where the same kind of thing happened - pretty much just the labels changing

I can understand that losing the choice is a bit frustrating though...I have no idea if they would "listen" to an email or a letter, but it might be worth a go.