There are a number of cross-assemblers for the 1802, but Mike Riley's ASM/02 is the newest, most capable, and runs on Windows and Linux PCs. He used it to write his Elf/OS operating system for the 1802, the source for which is posted on his Github pages (referenced elsewhere in this project). ASM/02 includes directives for producing code for various 1802 hardware platforms, including the MemberChip Card.

The cosmacelf community https://groups.io/g/cosmacelf/topics has been actively fixing bugs and adding features to ASM/02 and Elf/OS. Tony Hefner suggests downloading it from https://github.com/arhefner/Asm-02 as it's being maintained by the group. Al Williams just posted an excellent instruction manual for it at https://groups.io/g/cosmacelf/files/Al%20Williams/Assembly%20Langauge%20for%20the%20ELF_OS%20and%20ELF_BIOS%20Environment.pdf

Al's work is basically a programming manual for the 1802 using ASM/02. It explains the charming eccentricities of the 1802 (what, no CALL instruction?), and shows how the assembler gets around them (to add CALL, and many other "normal" instructions).