MIT will accept a recommendation from any of the disciplines it considers as fulfilling the Humanities, Arts, and Social Sciences (HASS) Requirement: MIT Course Catalog: Undergraduate General Institute Requirements
But to answer your question, yes, you must submit a letter of recommendation from a teacher in this area. It won't work to submit two letters from the math/science area.
It's fairly common for students to feel that they're in the position of asking for letters from teachers who may not know them all that well. Especially if you're in a huge public school where you are just one of 40 students in the classroom. Part of your task is to prepare written materials (resume; c-v; "brag sheet") to educate the prospective letter-writer about your skills and talents and to arrange a face-to-face meeting to discuss why you think you're a good fit for MIT.
The ideal letter-writer is not necessarily the person who knows you the best; sometimes it's the person who is most experienced at writing really strong letters. Your task is to find that individual, provide that person evidence of your strengths and commitment, and convince him or her to write a supportive letter on your behalf.