Add Entry Button Not Shown When Overriding Entry Sources
The New Entry button is not being displayed as Craft is not seeing my sources as containing publishable entries.

The Craft JS object contains a list of publishableSections which is checked by craft.js using this.getSourceByKey('section:'+section.id). Since my sources use a custom key value they are not included in this list.

So I have resolved the problem by adding my own New Entry button.