As far as the testimony of sir william muir, you could google it I am sure or find it on Islamic sites. Ahmed Deedat also had the quote in his book "is the Bible the word of God?". I can find it for you if you need it still or if you can't find it, inshaAllah. The Quran it self was written down during the time of the prophet (pbuh) and this was how it was to be arranged. However, the Quran wasn't on one sheet of paper but it was written on scattered pieces of palm leaves, large bones of animals and anything that was at hand. It was written down on those materials and it wasn't compiled and made into book form until the time of Caliph Uthman, about 22 years after the Prophet(pbuh). But the entire Quran was already written down, verified and memorized during the time of the prophet. Every year during ramadan the entire Quran would be recited and verified with the angel Gabriel. This was to assure that they had it right. It was during the time of Uthman(ra) that the manuscripts were compiled and made into book form. All the hafiz were brought and no one disagreed about anything. Everyone was in agreement that this was the Quran. Muslims have never fought each other or went to war with one another over the authenticity of the Quran.
Unlike the Holy Bible with all its controversy and fighting, the Quran has no such history and it has always been available to the people and in their hands. In the case of the Bible, it wasn't until recently that it became available to everyone and for over a 1000 years Christians had no idea of what all their scripture contained. It was considered "property of the church" and only priests and clergy could read it freely. This is not the case with the Quran and we never had any issues or wars over its authenticity or availability. Muslims may have fought at times over power but never over Quran. Furthermore, I recently learned while watching a documentery on Salahaddin Ayoubi, every one of his soldiers had a pocket size Quran with them and would read it. This amazing Subhan Allah because this shows just how our scripture has always been in the hands of the people and available to everyone.
As far as surviving copies of the Quran, the oldest that I know of are the ones in Istanbul Turkey, and Tashkent Uzbekistan. However, there are old copies in Cairo Egypt and one in a museum in Britain too. There are survivivg manuscripts from very early times but whole Quran's the oldest that I know of are the above mentioned ones. Also keep in mind that Quran is in Arabic and this is a living language which is still spoken today. The Quran is "recitation" and it is something that is to be recited out loud and this shows how it will always be the same. You could take a Quran, hide a few verses and bring a hafiz and would right away notice it is not the Quran. Whether we remove or add, it would be noticed and the greatest proof to me is the memorization of it, word for word and identical. The Bible, with all due respect, is not such a book. It isn't something expected to be memorized, recited and protected. To this day Christians have not always agreed on the same scripture, but Muslims all know there is only one Quran and no translation is the actual Quran except the Arabic original and Muslims would learn Arabic to know the Quran.
I will try to get you quotes and testimonies by western historians on the authenticityof Quran inshaAlla if you need some. Let me know bro.
wa salaam,