Hi!
I have the same problem with mine right now. I've been looking around online and it seems like the LCD and digitizer are glued together so you'd want to buy them together. I typically buy phone parts from Amazon because it seems to be the most reliable with the most reasonable prices, but you could get them anywhere, really. I wouldn't suggest getting something cheap, but there's no need to get an expensive name-brand. If your phone is under warranty fixing it yourself will probably break it, so just make sure you're prepared for that.
I hope that helped :)