I have found a pair of worn and grubby looking silver-hawk boots by the scoreboard at the Duel Arena.
I have given them a polish and inserted some new insoles.
I can only assume poor Biggy took a crushing defeat at the arena and must have stumbled home after the defeat dazed and confused thus forgetting an important part of his uniform.
I have left them with the Sergeant-at-Arms at the clan camp in Falador