Though I have to wonder why you need it. I hope you're not planning to reformat/overwrite a broken Tetris disk you've imported, .dsk files are not a 100% accurate copy of the disk contents, not to mention that many of them are cracked.
I hope the game (the data ) is damaged not the disk itself! because in the latter case you need to get a new disk (with label!!) I hope nobody has bought this yet
I have the original disk and ROM version. They are in Spain and I am in Germany... I think I bought them to you long ago. But there is no way I can have an image now...
About the legal/illegal issue: ask better in other forums. Here, you are not supposed to ask for any software @_@ since you are supposed to ask for something you don't have... (even if it is not true)
Also a dsk file is only good if the original disk plays nicely/works like the standard prescribes:
so no extra tracks, no fiddled sector headers, no extra tracks, no illogical sector numberings etc etc.
Or simply put, a dsk file can never ever contain the data that you need to correctly recreate any possible copy-protection on the original disk. So overwriting the original disk with a dsk image, might even break the program since you will destroy any possible copyprotection, making the program think it is an illegal copy (even on the original disk yes)