First, how I can get those three ref letters if I have lost most prof contacts from my undergraduate school? Second, what if my current employer wont be able to write letters for me, what else I can do? Thanks alot!
Tamp down any anxiety and write an email to any professors you think could remember you. Remind them of how well you did in their class, any interactions you had with them, and how you use what they taught you at your current job (if you do).
I’d also include a link to your LinkedIn profile so it has your background and a picture of you to help jog their memory without it being overtly obvious that you are trying to jog their memory of who you are.
If possible, drop by their office hours to visit them in person.
Generally, professors are OK with this. They may have you write something up for them with details of any interactions you’ve had with them that they can build off for their letter.
^This. Professors are used to writing recommendation letters for students who they may have last taught 2-5+ years ago. Just write a letter explaining who you are, your former relationship with them, and what you’ve been doing in the mean time. LinkedIn profile is a great idea, particularly with the picture. Attach a resume and, if possible, a draft of the personal statement you are writing to programs.
Most academic programs don’t want a recommendation from your current employer, anyway. They want people who can speak about your potential to succeed academically.