I'm not in the sports management field but had a handful of good friends from college in it. They've been able to land good jobs post grad so I asked them what they had to say, I'll summarize what they sent back.
1) Go to your professor's office hours. They've been in the field for years, they know tons of people and most will be more than happy to write a letter of recommendation or put you in touch with someone if you're on good terms. 2) Assuming your university has an athletics program, try to get on as a manager or some sort of volunteer for one of the sports teams. Coaches and athletic department staff's will also know plenty of people in the field. 3) Hit up each and every job fair your department hosts. I can echo this sentiment as job fairs are what put me in touch with the company who hired me out of school. Nowhere else will you see a room full of people who are trying to convince you to come to their company. Take advantage of it.
I hope the above helps!