It comes from hearing the Word of Christ. Faith comes by hearing. The miracles, Jesus does when and where he pleases. And it isn't a matter of believing more so Jesus can do more. It's trusting Jesus even when there are no miracles, when He is despised and rejected, powerless and dead on a cross.
Faith born of miracles needs miracles to feed it and keep it going.
Faith born of Christ, needs nothing but Christ. There were a few in the synagogue at Nazareth who believed in Jesus, a handful who hung on to His words, who were not scandalized by his ordinary, everyday humanity. Jesus always has a few believers, wherever he goes. Wherever His Gospel is preached, wherever His sacraments are being given out, there will always be a few believers. And He reaches out His hands and touches them and heals them.