To get stages, you can browse the net, as many people edited their own stages for this wonderful game. Eg., you can go here:
http://videogames.donkeyrol.co.uk/index.html
Look up the MSX section, there is a link in the KV2 article with KV2 stages I made a long time ago

This is only an example.
To handle *.dsk files, you may use a great piece of software available here:
http://members.chello.at/lexlechz/software.html
that will let you manage files in your PC, also transfer them to a properly formated floppy disk to use them in your MSX. Even, you may use an emulator for a quick run. My experience tells me, however, that nothing better than a real proper MSX to play King's Valley 2, the timing when jumping/doing actions is just smoother in the real machine.
Greetings!