Benzie Design (USA)
Canadian Felt Shop (Canada)
Dandelion Fabrics (Canada)
Gingermelon (USA)
The Felt Pod (USA)
Tissue and Decoupage Paper
I don't do a lot with decoupage at the moment, but I have found Ninny's Napkins has a great selection of paper types and patterns! And they're located in Creemore, Ontario.
Doll Hair
I have purchased mohair and ramie fibers from Divinity Fibers to use for doll hair and was quite impressed with the selection! They are located in Quebec and do have great shipping rates to the US.
Dollmakers Journey also has a nice selection of natural doll hair fibers, I've purchased their mohair.
Doll Making Tools
In Canada, Bear Dance Crafts has some items (I've purchased long needles and blush blocks), but she really is more geared specifically towards Waldorf dolls. She also has doll joints but I haven't tried them yet.
If you are located in the USA, you're lucky with all of your options (jealous!). I've got doll skin fabrics, hemostats, tiny turning tubes, etc from Dollmakers journey. I'm still on the hunt for a good source of mohair fabric..
When I took a pattern drafting course in February 2022, our instructor swore by Richard the Thread in the USA for the best fabric tracing paper EVER. Don't get confused, their specialty is corset supplies, but have a look around - they have some really great overall sewing supplies available!