Data amount for a very simple chatbot
Crowdsource your results. 

Your problem is very similar to writing Amazon Alexa skills. Creating intents, utterances and slots for Alexa skills. One of the recommended methods for developing this section of Alexa skills is to simply ask your friends and peers how they would go about asking for a given outcome. Crowdsourcing your inputs will give you some robust results because other people may think quite differently than you. I would recommend hopping into whatever Slack/Discord/chat channels you belong to and asking there. There may be more formal sources for such information out there but I am not directly aware of them.