I must admit I'm confused about what you are looking for.
If you are looking for some way to have mass storage without investing in atari kit then I guess I understand what you are looking for, but it doesn't seem to match your subject.
If on the other hand you are looking for a way to use disk images on atari hardware without first converting them back out to physical disks, then that does exist. However I don't know where to download it.
There is an Atarian in croatia that goes by the nick of VUK, he shows up on #atariscne on irc from time to time. He has a program that he has written that loads the MSA files into a RAMDISK that the atari sees as a physical disk drive. Can be used as an ACC or PRG.
But as I said I don't know where you can get it from except directly from the author.