re: I have never seen it - neither 'Canader'
but it's not common usage is it .. not yet anyway ..
google returned lots of links to Chick Corea the jazz muso, but yes there was also this opiniated page about the C/K spelling -
the American "K" spelling is offensive from a historical standpoint (remember "Peking" and "Canton"?);
violates western rendering conventions; suggests a lack of sophistication toward Corea; and by connoting naiveté, imputes a lack of sophistication to Corea and its people.
The Corea rendering will ultimately become universal when more Americans are educated as to the offensive and relatively recent origin of the "Korea" rendering.
gee, I wouldn't have known Phil was so sensitive to political correctness .. ;)