what is the oldest existing copy of Daniel 9:24-27, and where could I find it? Thanks!
This will not answer the question completely but provide some information. A complete list of the Dead Sea Scrolls is found here. https://en.wikipedia.org/wiki/List_of_the_Dead_Sea_Scrolls
There are numerous fragments and incomplete scrolls of Daniel. Frustratingly, none contain the text of Dan 9:24-27, although, earlier parts of the same chapter do exist amongst the DSS.
All these Daniel MSS documents date from about 140 to 90 BC (??) and clearly demonstrate that before age and decay had its effect, the book of Daniel then was essentially as we have it today.