Several of my friends are embroiderers and they use tacks to fasten the fabric to the stretcher bars.
Try www.berlinembroidery.com Click on "embroidery supplies" and then scroll down to "embroidery tools". You will see brass tacks on the list. There is also a kit which has a pusher for inserting the tacks. Will they do for your purposes?
Tanya Berlin is in Calgary, by the way, and if you are in that area you may be able to go and pick them up.