Did some searches and nothing came up. There’s lots of .17 cal variants out there, but haven’t heard anything about 12-14 cals.
Are these shells you found in a old house? Storage unit? Great aunt Gertrude's house?
Link at the Qual-Cart site? I’ve heard of .10 Squirrel and .12 Squirrel. Nothing about Blakefield.
I never heard of them...
I expect that if anyone knows about them, someone here would:
http://www.saubier.com/forum.html