A large portion of those wads in red are actually here on the MB, allow me a moment to link them...
BossRewards.lua: https://mb.srb2.org/showthread.php?t=42412
Silver.wad: https://mb.srb2.org/showthread.php?t=41391
tailsCD.wad: https://mb.srb2.org/showthread.php?t=41110
S3KShields.wad: https://mb.srb2.org/showthread.php?t=42090
SaturnsDropDash.lua: https://mb.srb2.org/showthread.php?t=41756
admintools.lua: https://mb.srb2.org/showthread.php?t=39363
HyperV2.lua: https://mb.srb2.org/showthread.php?t=39464
peeloutv4.wad: https://mb.srb2.org/showthread.php?t=39135
As for the things that aren't linked... well, blame what I like to call the "underground" modding community, there are mods that aren't released publicly on the MB due to being either illegal or unapproved for releases.
EDIT: TO ADD INTO THAT... How come the wads that you did download are in the Doomseeker folder and not in the main SRB2 folder? Using wadseeker isn't exactly useful for SRB2 as there isn't a SRB2 site that supports wadseeker-like sites. Alongside that, SRB2 wads that need to be available for you to play with have to either be in the SRB2 folder or the DOWNLOADS folder inside your SRB2 folder in order to be considered "obtained".
I did not know abot that, and it worked when I've put the files in the folder, thanks for that too!for you to play with have to either be in the SRB2 folder or the DOWNLOADS folder inside your SRB2 folder in order to be considered "obtained".
To simply explain, people make their own mods that they don't/can't publish to the MB, their reasons are well... their reasons or their mod may break Submission Guidelines that would automatically prevent it's release. Check the signatures of a lot of users here, they can link to different websites that have some of those unique wads or Discord servers where users might pass their wads around in.