We don't have separate resistors for sale. The resistor/filter is built-in to the ballasts for BMW.
But i still think you should try the relay harness first. A guy in UK bought our BMW kit for his 2005 volvo, and it also flickers and then shuts down. Another HID seller on the volvospeed forum told me that for newer volvos, the resistor will do nothing good. And Relay harness is the only way to solve the
problem. So, even with the resistor, you'll still need a relay harness, so why don't you give it a try first?
btw, do you get "check bulb" error message?