Darwin pilot supplies?
 

Is there anywhere in Darwin that supplies maps, shirts etc these days?

Anyone? I'm heading up but not sure if I should make the drive accross town to get new ERSA here.

Darwin has very little by way of pilots supplies because online stores, coupled with pretty good freight delivery systems right across Australia, will provide virtually everything you need.
The market for pilots supplies in a place such as Darwin is too limited for anyone to run a dedicated pilot supply shop - even as part of a wider operation.
Either drive across town as you suggest, or go to Clearprop.com.au or FlightStore.com.au. The online stores will deliver to your door unless you are located in some exceptionally remote spot.