As the Osborne is a pretty standard CP/M machine, any CP/M software will do, so look out for CP/M users (/groups) - there are plenty. In Europe especially, since the Amstrad CPC series gave CP/M a late boost.
Just keep working copies of the OS to boot. Disks can still be bought new and properly stored drives will surely work for a few more decades. Also, with its serial interface, everything needed to transfer new Software onto (new) disks is on board. I'd be more worried about the built-in screen or plastic parts.
If you really want to replace the drives, there are several designs, kits or ready to use flash-to-Shugart replacements available. Some are quite luxurious systems like Floppyflash.