Well ... you can look on eBay. There are usually screens for just about every phone for sale. But one of two things will happen:
1) You'll buy a screen, take yours out, replace it and the phone will be working.
Or, 2) (and much more likely unless you've worked on cellphones for a while), you'll find a tutorial, follow it exactly, have a new screen on the phone but the phone won't work. You'll come here asking what you can do and most of the advice will boil down to what I'm about to tell you now - save yourself some money, Take it to a repair shop and pay them to replace the screen. They that's the only repair you'll be paying for. You won't have to pay them to fix what you broke.