Using dojox in a custom widget

I'm struggling to use one of the DOJOX libraries in a custom widget.

In my require section I have written:

"dojox/geo/openlayers/Map"

but I get a script error saying

GET http://localhost:8080/mxclientsystem/dojox/geo/openlayers/Map.js?[some numbers] 404 (not found)

When successfully loading the app I have checked what's being loaded in dojo and dojox/geo/openlayers/Map is not included (some dojox libraries such as dojox/date/buddhist are there and I can load these in).

So how do I get other dojox libraries to load into a custom widget?

I've downloaded the library I need from the dojo website but for some reason trying to load it as a package is not working; Mendix insists in looking for it at the URL above and it's not there.

Any insight? This has cost me nearly a day so far.