This type of thing?
Only model I'm aware of that's easily available right now. Assuming an external model would be appropriate in the instance you are attempting to replace an internal drive that is no longer available?
The freecom traveller model is self-powered via the PC-Card bus (type 2) port so will use laptop battery and won't require additional a/c power supply when on the road. Also, Scan sometimes feature this drive on their 'Today Only' discount page so might be worth checking from time to time.