Real paint store whatever. Just go anywhere that sells paint, and buy a
can of "white" paint. Not "off white" or "cream" or "eggshell" or any
of the hundreds of other shades of almost white paint. You will
doubtless find dozens of "white" choices too -- gloss, semi-gloss,
super white, pure white, etc -- pick whichever one you think matches
best.

-Kevin