Although you don't mention Swissport - they certainly have part-time contracts - normally around 20 hrs per week with extra if desired.
Also, you don't say what job you are looking for : C/I / Ramp / Disp, however I'm sure most handlers have part-time for all positions however you would need to be realistic and not expect to work say 1000-1500 for 4 days a week as this would be unlikely to cover peak periods for many which is when they need the part-timers.
Hope that helps.