Maybe I'm totally dense, or something...?
cvs -P :pserver:anoncvs@anoncvs.netbsd.org:/cvsroot co -R netbsd-0-8 src
cvs -d :pserver:anoncvs@anoncvs.netbsd.org:/cvsroot co -r netbsd-0-9 \
src/sys/kern/kern_exit.c
(note I changed -P and -R to -d and -r respectively)
cat src/sys/kern/kern_exit.c