Well i did a quick search in google.com and found that there really isn't an official keyboard and mouse combo out yet but IGN says that there will be a free keyboard released with Phantasy Star Online you can see the article at
this link but they still arent saying anything about a mouse and microsoft said that they wouldnt release a keyboard but they obviously now have changed there mind and might release a mouse sometime in the future too, but anyway the only other way that i was able to find was to do some cutting up of a controller cord and patching together a keyboard, but i'm pretty suspicious as to how well that would really work, so good luck, i hope this helps.