Since you're in the market for a replacement, might as well look for an RPC-1 drive for DVD region-free goodness. Other drives Apple has used in the past include:
* Matsushita UJ-815/825/835/835-E/845/845-E/846
* Pioneer DVR-K05
They should be usable in the PowerBook G4 (AlBook) series. Refer to
this list of other RPC-1 drives used in the PowerBook line.
MCE Tech also offers SuperDrive upgrades. They list an
8X DL DVD±RW burner for $99 (exclusive of optional upgrade service). I don't know what kind of drive they use, though.