On the download page https://mikrotik.com/download only version 2.7 for the CSS switches are available.
There are still lots of old 260GS/GSP around, where is download for these (1.17)?
Good question. I have one of the RB260GS switches in service.
Looks like 1.17 is there now. In https://mikrotik.com/download
https://download2.mikrotik.com/swos/1.17/swos-rb260-1.17.lzb