Many quilt stores will also make up their own scrap bags too. Quilt shops tend to sell fabric in set sizes, metres or yards, fat quarters, half metres, etc.
As well as scrap bags I’ve also bought lucky dip parcels from quilt shops as well. It all depends on what kind of a quilter you are whether you will be attracted to a lucky dip parcel or a scrap bag.
If you’re not local to any good quilt shops but you would still prefer to buy from a small business Etsy can be a good option.
Another online option for buying inexpensive fabric is to search for ‘deadstock fabric’. Deadstock is a term largely from the fashion industry but it can apply to any kind of fabric.
If you like working with vintage fabrics or vintage prints, thrift stores can be a great way to save money.