like said many times here, there are 2 "wup installable channel" versions.
They are BOTH "wup" format and need to be installed with WUP installer.
One is legal and can be found on this forum, and is only a simple "vWii system menu booter" modded to boot UNEO vWii channel instead of system menu.
ATTENTION : you need UNEO vWii channel forwarder installed on your vWii NAND, or else the Wiiu Wup channel can't "boot vWii UNEO" if you don't even HAVE vWii UNEO !
WiiU -> vWii -> UNEO -> SD -> Boot.dol -> USBLoaderGX
This one run in "vWii mode" and has USB drive enabled. YOU CAN PLAY WII GAMES !
How can it be so hard to find it? it's in the FIRST POST OF THE OFFICIAL USBLOADERGX THREAD !
One is illegal to share and that's why you don't find anything.
this one need to be generated by the end users with teconmoon Script injector tool. you'll obtain a "WiiU Virtual Console Wii" channel (not a vWii booter!).
with this one, you don't need to hack vWii, you don't need to install vWii UNEO forwarder channel on vWii.
WiiU VC Wii -> USBLoaderGX
OR
WiiU VC Wii -> SD -> Boot.dol -> USBLoaderGX (SD required if you inject the forwarder's dol into the wiiu channel instead of the loader's boot.dol). injecting the forwarder's dol is recommended ! so you don't need to update your wiiU channel on new loader's release, only the dol on SD.
This one run in "WiiU mode" and DOES NOT HAVE USB ! only SD card is possible and therefore NO WII GAMES ! only gamecube games.
the only purpose of using this channel is to get a nice interface for gamecube launching for nintendont and being compatible with the WiiU gamepad. (playing gamecube games on the WiiU gamepad).
If you don't care about playing GC on WiiU gamepad, or expect to play Wii games, then THIS IS NOT THE CHANNEL YOU NEED !
Both need CFW with signature check patched out in order to launch them, because they are unsigned channels.