I think you can still find it hosted at other sites by doing a web search for "Ketman Assembly Language Tutorial" or "asmket16.zip".

I also just created a .tar.xz file of my own copy of the tutorial and uploaded it to:

https://www.datafilehost.com/d/6d9086c8

I also did a base64 encoding of the same .tar.xz file and pasted it here:

https://bpaste.net/raw/2521d4e2a230

The sha256 checksum of the .tar.xz file is:

41e5d16b2e0d15f67535d725baa2fa2fec00f65003e4745b60a3fb082111f5ff

Please note that this is not an official version of this tutorial. It's just what I had lying around on my disk after who knows how many years. Use at own risk.

If you want an official copy, you could try contacting the author at btketman@btinternet.com