Here is a list of shops for craft shopping/supplies in Brussels. Since the information might not be accurate at the time you view this post, please always check their website.
[will be updated]
Shopping Center City 2
Mo – Sa (10-19; Fri – 19:30)
This is a chain of shops; you will find them in multiple places in Brussels (and Belgium). At first I didn’t realize that they sell craft supplies, because they also sell clothing and accessoires. Veritas sells a modest selection of fabric, yarn, sewing supplies, beads, crochet needles.
Articles de Coutures
Boulevard Anspach 146
Monday – Saturday 10:00 – 18:00
A shop that sells yarn, fabric, beads. They seem to have a wider selection online.
Not really craft supplies shops but when you are luckily they sometimes sell craft supplies.
Also a chain of shops. They mostly sell very cheap clothing, but they also have a selection of cheap yarn and knitting/crochet needles. Sometimes they also have card stock and stickers.