Hello Julie,
I think you can use pulldata function. You can create lat and long values along with all possible zip codes in csv, and extract lat and long where user input zipcode matches with the one in the csv file. The lat and long information can be stored under two double fields or send it to geopoint as x,y attributes. Since there will be one lat and long for each zipcode, there may be duplicated points created potentially.
Cheers,
K