I know there's a post about USPS with MarketPress but alas I'm not in the US and neither are my clients.
I'm happy to have crack at creating the plugin, but would like to have some hints on any hooks and filters (I think thats what they're called) to create shipping options.
Maybe even a "vanilla" shipping module - where you add the api settings for the desired postal service. Just a thought.
Loving your work by the way, You've saved me many a headache in the last couple of weeks.
Edit: Ok I found this post https://premium.wpmudev.org/forums/topic/marketpress-international-shipping-different-rates-per-item and will start having a play with the plugin-template file