Which stations can I buy bullet train tickets from in kyoto.

I am currently in kyoto and need to buy bullet train tickets to Tokyo. My closest station is sanjo and the ticket office told me I can't buy from there.

Researching online ithink I can only buy from JR line stations however I'm not sure which these are and the ticket officer couldn't understand me.

Can anyone advise closest station to sanjo to buy bullet train tickets

by SeveralLetterhead