I actually looked this up a bit ago. Mikro Assembler came on cartridge. It is a bit of unobtanium, and I am not even finding a reliable image to run from an Untimate II+ or Easy Flash.
HES MON64 included a simple assembler, and that is a cartridge as well. But I am not sure if that is what you are looking for.
This is the Documentation for "The Fast Assembler" V3 by Yves Han, taken from Compute!'s Gazzete Issue 31 and also available in Best of Compute!'s Gazette, ...
I used Hypra-Ass, published by the German magazine 64'er. But when I got my first PC/XT, the first thing I did was creating a cable between the Userport of the C64 and LPT port of the PC. Then I wrote a communication program to exchange files and the I wrote a cross-assembler on the PC. Which I'm still using......
Thank you Ruud......if anything...I learned a new word today!!
Hypra-Ass can be translated into -> Hyper-Ass....
which means 1- hyperactive donkey or 2- some individual
with personality of an "Ass ^%$#" who is frantic about
everything or 3- a typical company CEO who knows
nothing about the value/effort of his engineers and treats
them as modern day slaves..........................
I wonder what any of these has anything to do with running an assembly program