If you are using maven you can just use a previous version number as they should all be in the FUSE maven repo
If you want to download versions with FUSE installers etc. I actually don't know.
Ah the installers is also in the repo:
eg here is for FUSE ESB 4.0.0 released last year:
You can click on parent directory and choose another version eg 188.8.131.52