How can I obtain an academic reference, if I have been out of college for a very long time?
Your situation now is very similar to my situation in 2001. I got all my references from colleagues who knew my recent work. Fortunately, I had been doing research-like work, except in an environment where it lead to product and patents, rather than papers.

The professor who supervised my master's degree project was still working, and I could have contacted him, but I felt that my recent work was more relevant than a project I had finished in 1975.

I made sure one of my references was academically well-connected, although working in industry at the time. The other two were a software engineering manager and a computer hardware engineering manager who could write about my range of knowledge as well as my research potential.