So I've asked two professors and my boss that I interned for last summer for recs.
One professor said he would write one for me, another professor said she had to write possibly 40-60 other recommendation letters so she might not have time (she's in charge of law forum and I wasn't in law forum). My boss from my internship offered to write one for me a couple months ago and I've contacted him about it.
So essentially, I have one for sure recommendation from a professor, one very likely from my boss, and one unlikely from another professor.
The current best case scenario is that I only get one academic recommendation. Should I randomly look for a professor I took previously (that I won't know at all) for a recommendation or am I OK with only one academic recommendation?
Necessary? No. Advisable? Yes.
Most committees or deans will not look too far askance at a non-law-prof recommendation, IF the other one is strong and both speak to the qualities of a stellar student.
If you can find another professor with whom you had some connection, and if the referee would consider three, you might consider "all of the above."
Crucially, however, while academic letters tend to hold more weight, what is more important still is the quality of the recommendation itself. A strong endorsement from a senior legal practitioner is better than a luke-warm one from any professor. (And, as you've described it, luke-warm is what you'd likely get with Prof #2.)