Air courses, if you mean filling up your marker tank then no course required though popular consesus is there should be.
if you mean the filling of dive tanks and larger air storage units then best bet is to look in your yellow pages for dive shops or compressor centres nearby who may be able to advise.
regards to markers, most markers come with a manual of sorts which give basic maintenance instructions, if your after a full tech course try the marker's manufacturers website as their may be some info on there.