All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all of his family and companions.
The vow to feed female teachers, is considered charitable act , and giving charity is of the pious acts which draw a person closer to Allah, so you (Questioner) are obliged to fulfill your vow since the Prophet (PBUH) said (What means): "Whoever vows to obey Allah, let him obey Him. Whoever vows to disobey Allah, let him not disobey Him." [Agreed upon]. Therefore, you should fulfill your vow as soon as its conditions are met and if you couldn’t, then you should make Ijtihad (Independent reasoning) for the purpose of fulfilling it; by trying to find the female teachers and give them the chocolate, but if you couldn’t, then you should offer oath’s expiation if you were unable to fulfill your oath in order to be on the safe side , as is the case in the Hanbali’s school of thought.
In this regard, Ibn Qudama (May Allah have mercy on his soul) said: ”Whoever made a vow to do an act of obedience and couldn’t fulfill is obliged to pay oath expiation, since 'Uqba bin 'Aamir (May Allah be pleased with him) narrated: "His sister took a vow to walk to Allah's House (for pilgrimage) barefooted. Then, she ordered him to consult Allah's Messenger (PBUH), so he consulted him for a religious verdict and the Prophet (PBUH) replied: "Let her walk and ride." [Agreed upon] in addition, Abu Dawood has a different narration as regards the last phrase:”Let her offer oath expiation” Al-Tirmithi added: ”Let ,her fast three days. Further, Ibn Abbas (May Allah be pleased with him) who reported the Prophet (PBUH) saying (What means): ”If anyone takes a vow which he is unable to fulfill, its atonement is the same as that for an oath.” [Al-Mughni vol.10 pp. 11]. And Allah Knows Best.