XB-900 got their own neck that are different from the other XB series (the imported one) but maybe you could fit one with some modification. There is an XB-400 neck available on ebay now, if you are good in mods you could buy it and try. I found a CB-14M (Classic Bass series) on ebay last fall and an XB-200 fretless in ebay also and the neck pocket of the CB accept the XB neck but the luthier got to carve the CB body to fit the strange bottom of the XB neck. Otherwise you'll pay an arm and a leg to fit any other neck that won't look as a XB original neck. Good luck!