So long as it has:
a) 6 volt DC regulated output (most are regulated), don't use a cheaper unregulated supply
b) correct plug type so it fits
c) correct plug polarity - this is absolutely critical and will probably be marked on the TV next to the socket
d) rated sufficiently high amperage to power it, I think 750mA is the rating of the official Casio supply
you'll be fine. There are plenty of third-party mains adapters which will meet those requirements (unless Casio have chosen a non-standard plug/socket type).