You have two ways to go on this. You can ask that the records be transferred to the other office, which by law he has to do at your WRITTEN request, and has a certain number of days to do it. You may be able to get around the wait period, and avoid problems with lost or missing films, if you go in to the office and sign for the x-rays yourself. If you ask for COPIES, he can by law charge you for the copies (there is a maximum charge allowed per film, can't remember what it was though).
The laws regarding patient access to medical records vary by state, so check with your states medical borad to get the full details regarding your rights. In some states, the Dr is under no obligation to release records to the patient and is only required to transfer them to another Dr upon written request. California happens to be one of the states where patients have legal access to their records, but it still can be a pain in the butt to get them.