How am I supposed to find 3 recommenders for grad school? So early onto my undergrad, I knew I had to find 3 professors to use for letters of recommendation, but given the schedule these professors have and how many students they have to deal with, I find it to be almost impossible to find more than 1 professor that can vouch for me, especially after that long gap between taking their class and applying for grad school during my final year. I can simply just reach out to the ones that I got an A in, but I'm not their only A student and they likely forget who I am.

Add in the factor of the professors not being able to reply to my email and you are left with stress. Can anyone help me figure this out? I feel like this is by far the most difficult aspect of the application. 

Also, how can you use professors for letters of recommendations if you decide to take a break between grad and undergrad?
First, I wouldn't make the request via email, although it would be a good idea to request a meeting via email to discuss your plans. We may not be able to put a name to a face from an email, but if you make a point of visiting and reminding them of the course(s) you took with them and how you did, that would go a long way in tweaking their memories. Second, come prepared. Bring copies of your transcripts, your resume (which should include work and volunteer experience), and a clear idea about what your plans are, including with who and what you plan to study. Finally, give the prospective reference time to prepare a good letter (a month is usually the minimum) and a clear deadline for when the letter is to be submitted by. 
(As a side note, I assumed your comment about professors not being able to respond to your email simply meant they hadn't gotten back to you.) Good luck!