I am not aware of a widget or shortcode that does that, but I will flag your question for the developers.
I have been answering your questions in regards to V1, but, V2 offers a new features that may be interesting to you.
Within the GD listings shortcode it is now possible to specify a location that exists in the Location Manager, and to call up a list of listings of one post type that are all “IN” that location. Several of the shortcodes could be added to show more listing types next to each other on the same page “IN” that same location.
Indeed this is how location pages work, essentially. Every location gets a page, and as many GD Listings shortcodes as are need can be displayed on the same page, of any quantity of post types. All those listings then show up on the map, albeit with a post type selector.