The filters are stored in the actual database, not in an external file that is easy to move.
Actually, I just looked through the settings table though, and if you are using the same version of PT3 on the other machine, you should be able to backup just that table of your database via pgadmin3 and then restore it on the other machine and it should be (relatively) painless.
It's going to be very similar to the process described in detail in
this post with one exception: instead of right clicking on the whole database, you want to expand the database (click the little + on the left), expand Schemas, Public and Tables. There are 33 tables. You want to right click on the settings table and back up that table. The backup window will look identically and the restore process is actually identical as well; it's just on the backing up side.
The only downside with this approach is that it will remove any saved filters on the other machine. It sounds like you have all of the filters you'd want on that machine as well though so that may not be that big a detractor for you.