Then you need to modify or pay someone to modify the import script to make the permalinks. What you are trying to do is impossible. The topic ids are all different. If you have users already using the community now you’re either out of luck or will need to throw away their posts.
Oh. Sorry. The import_ids should be in the database. You can write a script to create the permalinks. You’ll need to look at some of the other import scripts for one that creates the redirects after the topics are imported rather than as part of the import topic function.