How do I make a sitemap per section?

We're building a website targeting two English speaking regions - EN-US and EN-GB, set up as:

site.com/en-gb
site.com/en-us

We created "duplicate" content types for each section, but with default url aliases setup accordingly.

We think we want a sitemap for each section - i.e.:
site.com/en-gb/sitemap.xml
site.com/en-us/sitemap.xml

...as they are effectively distinct sites, just sat under the same domain, making management of the content easier for admin.

The content under each path will be distinct/unique, so using langhref won't work for this scenario.

Can anyone help me with how to do this - or tell me there's a better way to achieve what we're aiming for?!

Thanks in advance

Andy