To support multicast over mobile IP networks, the IETF proposed two schemes, namely bi-directional tunneling (MIP-BT) and remote subscription (MIP-RS). MIP-BT provides mobility by establishing bi-directional tunnel from home agent to mobile node's care-of address. Although it does not require multicast tree reconstruction, it suffers from redundant routing that causes packet delivery delay and network bandwidth consumption. On the other hand, MIP-RS provides mobility by reconstructing multicast tree when mobile node enters a foreign network. Although MIP-RS provides shortest multicast routing path, it requires the reconstruction of entire multicast tree in case of source mobility and causes service disruption during the process of handover. To cope with those problems, we propose new source mobility scheme that enjoys the advantages of MIP-RS and provides seamless handover with the help of proxy router, which assists handover by swapping network addresses and conducting packet forwarding. We examine the deployment issues of the proposed scheme over the Internet and evaluate the proposed scheme from the viewpoint of routing distance and network bandwidth consumption through simulation experiments with various parameters, and then clarify the effectiveness and efficiency of the proposed scheme.