Good luck finding a Pioneer 115d. They have been out of production for quite a while.
That Pioneer isn't an external drive, but you can get an external enclosure for any internal optical drive and hook it up to your laptop with a usb cable.
There are also some external drives you can consider, though I don't recommend the slim types. Get a half-height external drive with its own power supply cord. Here is an example: http://www.newegg.com/Product/Product.aspx?Item=N82E16827106338 Note...that's only an example. There are others available from Plextor, LG, HP and others.