The last time I installed a new disk image on an SD Card for the Pi I had to use the Win32DiskImager util on Windows. Since I primarily use a Mac that took a few additional steps to get a working SD Card.
Use username of the remote share. You’ll be prompted for the password for the remote user:
mount -t cifs -o user=username //ip_address_of_remote_server/sharename /local_mount_point
Over the years there’s been a few different people who have designed and built custom peripherals for the Atari ST, like SD Card readers and Ethernet adapters. These were usually sold as one-off custom orders, and built on demand. It looks like there’s a company called Lotherek that’s started to manufacturer many of these with permission from the original developers – check out their site here.