Very few airlines except the legacy carriers handle themselves these days. For most it's a case of remaining profitable and the only way they can do this is to outsource to the various handling agents that currently exist.
The best option is to write to them directly and in most would mean starting at the bottom and working your way up.
Like you i too am passionate about aviation but it's becoming clear that experience and age isn't always a good thing. Biz jet operators want experience Bizjet folk. They're not that keen on Charter & Ad-hoc ops specialists like myself.
I wish you luck in your search and if you do come across any positive leads am sure there are a number of us on here who would be interested.