From the CFN website: Volume 117, Number 2 (2003) onwards. (Last four issues are only available to OFNC members and subscribers.)
From the Biodiversity Heritage Library:
Hard copies of Volumes 109 (1995) to 123 (2009) are available for FREE*.
Hard copies of Volume 124 (2010) onwards are $10/issue*.
Special issues of The Canadian Field-Naturalist – free*
“The history of the exploration of the vascular flora of Canada, Saint-Pierre et Miquelon, and Greenland” by James S. Pringle
“A life with birds: Percy A. Taverner, Canadian ornithologist, 1875–1947” by John L. Cranmer-Byng
*Plus shipping fee if mailed