Impossible may be an overstatement. I have seen one or two in person (it perhaps helps that I was at KansasFest) but they were priced like premium or rare APple II upgrades -- the superdrive kit with a card and one drive was $450 or so.
I considered picking one up, but instead for about $80, was able to pick up a card that lets me use a CF card as a hard disk in my IIgs. (*I am terrible and have forgotten the name.)
1.4-meg floppy storage is definitely uncommon and is probably not something that the everyday Apple II user bothers doing.
There's also the FloppyEmu, which won't work on the older APple IIs as far as I know, but which adds SmartPort emulation so you can use it for Apple IIgs flopy and hard disk emulation.
Tools like the UNISDISK and the floppyemu are some of the neater things going on in the Apple II scene at the moment. I have like five or six 3.5-inch floppies that I use sometimes, but by and large, my IIgs gets software through its serial port, using localtalk.