I'm trying to get my platinum trophy and this is one of the last things in my way. I don't like stealing that much and rather be fighting. Is there any way to speed things up and how long would it take?

just do Numbers jobs.

So I don't have to do a heap of different ones?

It's based on how many jobs you do in each city rather than the jobs you do, so no you don't have to each mission a certain amount of times, you can just do one type continuously.

Sweet, thanks.