Locations using GMAP
It's not totally clear what you're asking, but here's a stab:


It doesn't sound like the data will be updated frequently enough to justify processing it on every cron run - you mentioned recent deliveries... what do you mean by recent? In the last hour? Last day? 30 days? Find the right balance based on the freshness of the data itself, and only update what's new, especially if you're doing it on every cron run.
Get the data out of Access in a reasonably ready-to-consume format - don't expose the ugliness of your Access data structures to Drupal. This could mean setting up a custom view in Access to summarize and reformat the data you need for Drupal.
Setup a scheduled export from Access.
Use Drupal Feeds to import/update the data from Access into Drupal, either on demand or periodically. 


HTH.