I just did a lookup and Zeppelin I, II, and III are still available to me. I did a lookup using a third party search service for the Spotify service, and all three releases are still showing available. What listening region are you currently in? If you use the Spotify desktop app and go to this Led Zeppelin I album page here: https://open.spotify.com/album/3ycjBixZf7S3WpC5WZhhUK is there a bubble window to the lower right hand that reads with a down arrow in it, 1 MORE RELEASE? Click the down arrow to show the other release, and this should take you to the Remastered release version of Led Zeppelin I. The releases of Zeppelin I, II, and III album pages all have this with a 1 MORE RELEASE available.
Just to help you locate these releases and make it a bit more easy for you, these links below should be the links to the remastered versions of Zeppelin I,II, and III: