I recently got a large batch of old Citadel decals, from the early 90, off ebay. Simple heraldic symbols such as you mentioned, in a variety of colours, both small sizes for shields and larger sizes that would fit small banners.
I planned to use them for the same reason as you, and tried one out on a banner, it was ok... I'm now going the route of designing and printing my own paper banners, so don't know when or if the decals will get used.
Have a search on ebay for 'citadel transfers', try putting 'fantasy', 'medieval', 'bretonnian' or 'fighter' into the search as well, they seem to pop up every now and again.