just checked the SPM website and it seems to work fine.
The standalone version of SPM is not accessible through a link like the standard version. Within the “requirements” section on the SPM12 site, you’ll find the following “Alternatively, a standalone SPM (compiled using the MATLAB Compiler) is also available and does not require the availability of a MATLAB licence (but comes with limitations).” . Following that link will bring you the SPM standalone wikibooks site, including information on how to get it: “A standalone version of SPM12 is available upon request for most platforms (Windows, Linux and MacOS 64 bit). Please contact email@example.com.” .
I guess there’s also someone who can share it with you. Alternatively, have you thought about using a docker container which includes the SPM standalone version? Here’s an example by @miykael, or just built your own using neurodocker.
HTH, best, Peer