For the hardware part, any usual USB 1.44 MB floppy drive from Amazon should be okay (in my personal experience it has worked).
For the software part, some distinction has to be done:
every Mac OS X < 10.6 is able to format/read/write HFS volumes, so your G4 should be okay!
More modern OS X, Windows and Linux don't have the ability to write to HFS volumes out of the box. So, IMHO, the best way to do that is passing through an emulator, such as
Mini vMac.
The steps are, more or less, these:
1) create an empty 1.44 MB disk image in RAW format (that is a file exactly 1,474,560 bytes long and full of zeros), or take the one supplied with Mini vMac (in the blanks-1.0.0.zip archive)
2) mount the disk image in Mini vMac
3) from Mini vMac, format the mounted disk image and place there all the files you need
3) eject the disk image from Mini vMac
4) transfer the disk image to a physical floppy (more detailed instructions for several OS
here)
Please, pay attention to the format of the disk image: the RAW ones don't require any skipping, while the Disk Copy 4.2 ones have an header of 84 bytes that has to be skipped.
As an alternative, there is also
hfsutils. You can use it on any modern OS to format/read/write HFS volumes, both on physical devices and disk images. But, in my opinion, it is quite uncomfortable, even if effective.