@hyoujinnn, may I ask how important completing this application is to you? Do you want to resolve this and apply, or fall short of completing your application? If resolved to overcome and finish this application, then read on. If not, then stop here.
All ROTC branches have a host of applications including Navy that are started but not completely finished by many candidates each year, who ultimately deliver an excuse instead of a result in fulfilling requirements of the application, or just don't see it through. It's designed to be a bit of a gauntlet and helps eliminate those that maybe aren't the right fit.
You could do the following:
1. Discuss this challenge with your NROTC application coordinator and confirm your options. If you took advanced math in 8th grade can that teacher write the recommendation? Surely you're not the first candidate with this challenge.
2. Call a meeting and if your parent is willing, come to school or zoom with you and your parent/ guardian to briefly meet with your counselor, school administration/ guidance leadership and math department chair to point out that this evaluation is a requirement and ask them how they as a team will help you to meet it. I understand some retirees stop picking up the phone, but all of your math teachers cannot be reached so soon after retirement? I'm annoyed with your counselor's described shrugging of his shoulders and ceasing to help - I believe more can be done to help you.
3. I would grab the bull by the horns here, and as noted nicely above network, use social media and find a way to reach these teachers. I would if the school won't help reach them very respectfully and directly via DM, text or a call. Check in on them (a common complaint I hear from recent retirees is that the phone never rings/ people don't ask about how they are doing), reminisce about how much they taught you, how you miss them/ are grateful for what they taught you, and talk about your dream. Ask for their help. I'd be astounded if all of them said no if you do this. But try the school approach first would be my recommendation.
Deliver a result, not an excuse, and as free advice, there are often alternatives even when someone in charge states "there's nothing else we can do" with an authoritative tone. You can choose to not accept this, if I were your parent I'd be pointing out that this evaluation is standing in the way of a potential career as an officer and tuition/ fees paid and I'd appeal that they help you fix this. I think they will help as long as you don't put your trust in your counselor who already told you he won't do more. This is too important to you to fall short over this. Advocate for yourself.
Good luck and thanks for your willingness to serve.
