Hi, I found a few Buxtehude scores on the website of the International Dieterich Buxtehude Society. It looks like they are the editions Ton Koopman used in his recordings. Here is the text for those scores:
Ton Koopman has recorded the complete works by Buxtehude. He makes available sheet music from his productions to all friends of Buxtehude. Many thanks to him!
Also, for another work:
Roland Wilson has recorded the Abendmusik “Wacht! Euch zum Streit” for Sony Classical, with Musica fiata and La Cappella Ducale. The sheet music for that production has generously been made available for the public by him, many thanks for doing so! The music may be copied for personal use. Any public performance must however be registered by the GEMA or any equivalent national performing rights association.