If your schoolCS to Math and Math to CS is at a comparable standingnot an uncommon transition that students might choose to themake between undergraduate and graduate schools you. You are applying to, this should be fine for Master's programsalso majoring in CS, which generally acceptso you are certainly a diverse pool of studentssuitable candidate. If it is not, I would consider speaking with at least one of thewill add that your own statement about why you want to study CS professors (perhaps the theory one), but I wouldand not pure math will also be applyingimportant here—try to less ambitious safety schoolsbridge the two fields in additiona way that is meaningful to you, and how the program can help you further that.
Now to answer your question, I find that there are two possibilities:
If your school is at a comparable standing to the schools you are applying to, this should be fine for Master's programs, which generally accept a diverse pool of students—although one might still wonder why you don't have any letters from CS professors. I am of the opinion that it is better to address it than let it linger. You don't need to explain too much, but just explaining that you worked closely with (Math professors) Drs. A, B and C on such-and-such projects is sufficient.
If your school is not at a comparable standing to the schools you are applying to, I would consider speaking with at least one of the CS professors (perhaps the theory one), but I would also be applying to less ambitious safety schools in addition.
PS. Be aware that you may not get a TA position at the time of admission. These positions are competitive, and in my experience, they are offered to Master's students only when there are vacancies after all the PhD students have been assigned. In general, they may not care all that much about your undergraduate TA experience, but it doesn't hurt.