At your boyfriend's arraignment, he will have to complete an interview with probation to determine whether he qualifies for a court appointed lawyer at low cost or no cost. The judge will then appoint a lawyer of he qualifies.
If your boyfriend cannot afford an attorney he can ask the court to appoint him a lawyer. He would be interviewed by the Probation Department to see if he qualifies for an appointed lawyer. If he does qualify financially the court would appoint him a lawyer. There are some great lawyers that take appointed cases.
Other than that you can ask individual lawyers if they would take the case for free, I however don't think that you will have much luck.
I don’t practice in your jurisdiction but I don’t think that there are attorneys who would take on a criminal case bro bono. This is, basically, because if a defendant cannot afford an attorney one would be appointed to him by the court at no cost. If your boyfriend doesn’t qualify for a free lawyer, you may want to reach out to the local bar associations and see if they can provide you with a listing of attorneys who would be willing to handle the matter at a reduced fee/rate.