This is one of the reasons that you will see multiple companies selling copies of older recordings.
Now, with that out of the way, an audio editing hobbyist with a particular fondness for Wagner, (who is well known to many that have spent the years on various Wagner forums and newsgroups), William Hong, has remastered and made available for free a number of "classic" Wagner recordings. Originally, as noted by A.C Douglas this was at first the original 1953 Kruass Ring (click here to read the original post). However, he has now remastered and made available the following recordings:
Knappertsbusch 1951 Bayreuth Parsifal:
Krauss 1953 Bayreuth Ring Cycle:
Jochum 1954 Bayreuth Lohengrin:
Kempe 1956 Berlin Meistersinger:
Karajan 1952 Bayreuth Tristan und Isolde.
Further information - and the download links - can be found at the Wagnerheim Forum