I there any way to find users based on reputation range or exact reputation.
I want to find my friend, I didn't know his name but only the first character and reputation.
Is this possible?
Use this query. I've set it so that it shows the top 1000 users(letting it select all slows it down and makes it fail many times) with rep between 200 and 300, with usernames starting with 'a'. You can twiddle the values if you want.
Too long for a comment due to the link, I have somewhat different idea.
Forget about name or reputation. If you have a picture that might be his profile picture, you can use Google Image Search to find him.
For example given Jon Skeet picture his profile is the first result.