I remember doing something similar a few years ago, I needed autocomplete for a shipping ports field, the data was too big though so I ended up using a csv file

I remember doing something similar a few years ago, I needed autocomplete for a shipping ports field, the data was too big though so I ended up using a csv file in an aws lamda function that filters based on the selected country and returns a much smaller subset. It lazy loaded after the user selected the country. To keep response times low I had to do a binary search on the raw csv bytes. It felt like I was reinventing databases but I liked the idea of it being self contained in a function.