Maybe retry after completely wiping out the file system with the maintenance menu if you have nothing important on the calculator : option 4 instead of 2.
Unfortunately, the discontinued ClickPad/TouchPad Nspire Docking Station seems to be the rarest, and thus more expensive than the CX/CM ones :https://www.ebay.com/sch/i.html?_from=R ... on&_sop=15
It's probably possible to build a replacement for cheap as it's just using standard USB chips, but rare and expensive also means less reverse engineering on it. And indeed, it hasn't been documented so far to my knowledge.
You've also got the TI-Nspire DataTracker/Connection cradle which is more handy and features a nice USB connectivity by still using some Dock GPIO contacts :
But it's even rarer.