Create a new blank file with 1.44 MiB:

$ dcfldd if=/dev/zero of=floppy.img bs=512 count=2880

Attach the disk image, but don’t mount it:

$ hdiutil attach -nomount floppy.img
==> /dev/disk2

You’ll get a device identifier back. After that, it’s the same as FreeBSD to create a FAT volume:

$ newfs_msdos /dev/disk2
==> /dev/disk2: 2829 sectors in 2829 FAT12 clusters \
==> (512 bytes/cluster) bps=512 spc=1 res=1 nft=2 \
==> rde=512 sec=2880 mid=0xf0 spf=9 spt=32 hds=16 hid=0 drv=0x00

Or you can use hdiutil:

$ diskutil eraseVolume MS-DOS "LABEL" /dev/disk2

And then you can use it in your VM, or however else you need.