How do I load the game on a 1541 Ultimate 2+ ?
As stated in the page above:
"The downloadable C64 digital version is designed for use with a C64 emulator – it cannot be used with an EasyFlash cartridge, 1541 Ultimate, or Turbo Chameleon."
Why is there no .crt file for download?
The game was developed for the GMod2 cartridge format and as such there's currently no way to run these files on the Ultimate. You would need to contact the makers of the Ultimate and ask for GMod support.