Scans_Daily

I remember a Comics Should Be Good article about this not too long ago. I THINK that Walker got the USAgent outfit and shield that belonged to Steve as the Captain, but Walker decided to quit as USAgent maybe around the end of West Coast Avengers and chucked it all into the ocean and it hasn't been seen since. John's used a whole variety of other shields since.
(Article here: https://www.cbr.com/captain-america-shield-new-york-bay-usagent/)

So the Captain's vibranium shield either blew up during the "exploding vibranium" storyline, or is still at the bottom of the bay, or was rescued offscreen and just hasn't been seen since AWC #102.