I think you are missing something!
1) You dont need to know where it is but this SQl should show you some information of them.
SELECT MSysIMEXSpecs.SpecName, MSysIMEXColumns.FieldName, MSysIMEXColumns.Start, MSysIMEXColumns.Width, MSysIMEXColumns.SkipColumn
FROM MSysIMEXColumns INNER JOIN MSysIMEXSpecs ON MSysIMEXColumns.SpecID = MSysIMEXSpecs.SpecID
ORDER BY MSysIMEXSpecs.SpecName, MSysIMEXColumns.Start, MSysIMEXColumns.Width;
2) You dont need to export it
3) Make a copy of the dB then you have a copy of the import spec. You can also delete verything else you dont want a backup of (tables/queries etc.) but I dont see the point in that, having a backup is a good idea.
If you need to make changes to it then you can make the cahnegs and than make a copy for you backup.
If you need to restore import spec from you backup you will first nned to delete the original and then import it again from the backup.
http://support.microsoft.com/kb/208991