You can purchase the items separately, but as i found out last night, when you try to separate the digitizer from the lcd screen all you end up doing is breaking the lcd screen!!
I had hopes on replacing just the digitizer on mine so I purchased one since they can be found on ebay for under $10 with free shipping, and am now waiting on my new lcd to arrive in the mail because i found out you cannot get the broken digitizer off of the good lcd without making it a broken lcd. I would suggest either ordering the digitizer/lcd assembly or at least both parts and then you don't have to do as I did and spend 4 hours on a project just to have to order another part and then wait for it to arrive to finish it.