Modify an existing Joomla map extension

I need some code added in a Joomla! map extension. One of my Joomla websites uses a map extension allowing to show gpx files with info and pictures on Google and/or OSM maps. My country's National Geographic Institution (NGI) makes its topographic maps available for use in websites by means of a view service. The specifications are available in an xml file. A special permission is needed to use their view service and I obtained that permission. Now I need someone to adapt the code in my Joomla extension so that my website users cannot only select the Google or the OSM maps, but also the NGI maps. I think this should be a fairly easy and small job if you're familiar with Joomla programming and maps concepts. If you're interested to bid on this project, you can contact me, stating that by no means you will make the modified code of the extension publicly available, nor commercially, nor for free, and that you understand this only concerns one specific implementation for which permission was granted. You'll be told which Joomla extension this is about, and where to find the view service xml file. That should give you all the information necessary to make a bid and to do the job if you're selected.