How did that happened? I see the phone has more than 10 central hit points. Anyway, that's not what we should be talking about.
First, welcome to the forum.
Second, i think that you can buy iPhone parts from bestbuy or ebay, but the main question like you asked is will u be able to change the parts by yourself? Personaly i've never had the opportunity to change iPhone parts but with my previous nokia phone, yes i had to change the screen 2times, and even though it was easy to change it, there was always some dast, really minors dast but noticiable inside, i hated it, finaly i had to take the phone to nokia care and buy a new screen parts from them and pay for the fix.
Here i beleive that you might be able to change the parts by your self of you have the equipments and watch a video about disassembling and assembling iPhone4 parts on youtube, but you will never be able to keep dast away from beeing inside the screen after you place back your new screen. If this fact doesn't matter to you then with patience and some little precision, you should be able to fix it, else try then to locate the nearest apple store in your area. That's my 2cent.
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