Finding nearest coordinate thats not in the mysql database

[hello dave]

For a project Im working on i need to store a coordinate for each user in a kind of map project, however i need a way of when creating a new user to find the nearest coordinate to a certain point that is not in the mysql database so that all the users have coordinates close together. For example finding the nearest free coordinate to (1000,1000). The coordinate could be stored in one column or as two separate ones for x and y. If you have any ideas how i could go about this i would be very grateful.