Mobile mapping is optimised for colour, which isn't available on any of the e-ink devices I can find, despite talk of colour e-paper since about 2013. Having played with black and white prints of OpenStreetMap via InkAtlas (and having reproductions of old B&W Ordnance Survey map) I can say that stripping out the colour information is hard, and really degrades the map; the old maps had less information than equivalents at similar scale, but were also less clear.
The reason you can't find a device with a GPS chip is that most e-ink Android devices are designed as e-book readers with some tablet functionality, and not as full-featured tablets or phones. The only device I've seen that definitely has a GPS and E-ink is the HiSense A5, which is apparently very hard to get hold of outside China. HiSense announced a colour version at CES, but it remains to be seen whether you'll be able to get your hands on one.
Trying to add GPS to an existing device is likely to be problematic, as most phones and many tablets already have a chip on board. This means that there's not much of a market for add-on devices, and they're unlikely to be fully supported