Replacement disk for G-RAID thunderbolt 3 20TB

I haven’t been able to find where and how I can purchase a replacement disk for the G-RAID thunderbolt 3 20TB. It’s obviously a 10TB HDD, but in the ‘accessories’ link on the product’s page I only see 4 options for what they call ‘spares’: 2000, 3000, 4000, 6000. Can anyone send me in the right direction or is it not possible to purchase spares or replacement disks for the 18TB, 20TB and 24TB models? If this is the case, what happens then in the case of a disk failure?
Much appreciated.

Here is a link to the 10TB spare modules: 10TB Spare

Thanks for the link Rydia. Is there also a link to a place in Europe? I live in Germany and would like to order it here and avoid long distance shipping, customs, etc.

OK, I already found one in Germany.

I need a replacement 8TB 7200rpm replacement for the G-Technology G-RAID 2 bay thunderbolt 2 raid array. One drive. Can anyone tell me part number or ordering information? Thanks. Roy