Uni career services are generally very available and very keen to work with students throughout their time at university - and, actually, they're generally also available to graduates for a period of time after they finish their courses. So, I think you're wrong both in times of the timing - finding a job shouldn't, ideally, be something you do nothing about until graduation - and in saying no help is available after that time.
I also think the idea that employers should offer you jobs 'based on your mark' is a rather odd one. Yes, some employers screen candidates based on degree classification - requiring a 2:1 for entry to a graduate scheme, maybe - but that's largely an exercise in thinning the numbers of applicants down. Other than that, employers are far, far faaaar more interested in your skills, experience, and attitude than they are in your grades. Getting, say, 75% overall is really only part of the picture for an employer, and expecting to be offered jobs just on that basis would be a pretty big red flag for them.