Recommendation? Birch Bark Supply

[Ten_Mile_Knives]

Hey, so I recently finished a Puukko-style knife with a stacked birch bark handle harvested from Northern Michigan. I would like to make more stacked birch knives, but I need a supply of bark more regular than I am able to get by driving 3 hours North. where is a good place to purchase either pre-cut squares for handles or sheets with decent areas of clean bark to make knife handles? I've seen lots of postings on Etsy, Ebay and one on KnifeKits.com, but I guess I'm looking for some consensus on the best source.