"No matter where [I] look, there's no kid as good as this"
Past tense verb + って has the same meaning as て-form verb + も. どこを探したって means the same as どこを探しても. "No matter where [I, you, etc.] look". You'll also come across だって, which means the same as でも. 俺だってできるわ = 俺でもできるわ。
やしない is being attached to the ます stem of いる ('to exist'), which is い. い + やしない = いやしない. You can find やしない in this site's dictionary.