I know if someone wants Ij180 3M and they have an image 20" x 12', then they have to eat the raw cost of the waste. I dont think you can get small rolls of that to keep in stock nor would you want to.
There are definitely some medias where keeping every conceivable roll size in stock is unrealistic, IJ180C is a perfect example. With something like wrap material, the only real universal common width is 52" roughly, so it's unrealistic to expect a wholesaler to have 24", 36", 48", 54", 60" etc. in stock when those sizes are never used. But with something like banners, a good wholesaler should at least have the volume to be able to nest various jobs to maximize medua usage and mimize waste, or stock roll sizes for common job sizes, i.e. 2', 3', 4' etc.. If you aren't able to do this, you're probably not really ready to consider yourself a wholesaler.
It's realistic to expect a wholesale client to pay for a few inches of waste material (say a 4' banner with 3" for hems... 51" on a 54" roll, 3" of waste). It's not fair to expect a client to pay for 27" of waste for a 24" banner (plus 3" for hems) printed on a 54" roll.