A solution could be to use the CsvBulkLoader
class, export regularly the Access db and importing it into SilverStripe via a custom CsvBulkLoader.
http://doc.silverstripe.org/framework/en/howto/csv-import
Or create a custom BuildTask
that fetches the Access database and update SS with the new data. This would probably give you the most flexibility and this can be run as a CRON job so you don't have to do it manually.
http://api.silverstripe.org/3.1/class-BuildTask.html