This got me thinking about my time as a teenager teaching myself assembly on my C64 (which of course used the 6502 instruction set). I was trying to recall the assembler I used and I finally dredged it out of my memory: Develop-64 by French Silk Software, a now-forgotten program that I used a lot. My mom ordered it for me (her credit card) and she mentioned that the person on the phone wondered how in the hell some kid in northern Canada had ever heard of them. Good times.
There are references to a "develop64_cracked" on a retro FTP server that's 404ing for that file; this RAR seems to contain the file was was on the FTP server.
Also, backspacing the file off the path in the first URL gives a listing of some other releases, but this file isn't listed. Woot.
I wish I could use bold for this line - THIS is how you keep data alive, people!! :D
Also for reference, the reocities link in the above URL is dead, but oocities.com works. Unfortunately the geocities paths are not in oocities' archive.
And these links were near the top of Google's results.