What kind of lightbulb goes into the popcorn cart model # CCP-509 and where can I purchase the lightbulb

Your Use Manual can be found here.

On page 4 of the pdf it indicates that an E27 40 Watt light bulb is used.

You should be able to purchase a replacement bulb in any lighting department that stocks a full range of light bulbs including appliance bulbs; this would more commonly be referred to as an oven light bulb.