Need references that cannot be coworkers, must be management.

I have worked at the same job for over 10 years. There isn't much management turnover, and ones that have left I haven't talked to in years! They specified it cannot be a coworker, it must be someone who does or did supervise you. My current boss would definitely give me a good reference but of course I don't want to give them a "heads up" I'm looking to leave. I feel awkward reaching out to people I haven't talked to in a long time. I have a few days to figure it out but I really want this opportunity, it is stressing me out!