I know there are tools on ticalc to disassemble an 8xp and its not too complicated to write your own wrapper on a z80 disassembler for them but how would one go about this for an 8xk.

8xk files are no more complex than 8xps, but in a different format. The data begins at file offset 0x4e and is Intel Hex formatted (which can be converted with many common tools, such as objcopy); the data continues until the last two bytes of the file which are a checksum.

For most apps there's only one page of data, so you'll get 16k of data at a base address of 0x4000. The app image begins with a header made up of variable-length fields. Each field begins with a two-byte header; if you interpret these as a big-endian 16-bit integer, the top 12 bits are the field type and the bottom 4 are usually the field length. The app's executable code begins immediately following field 0x807.