2nd hand Leather jackets...
Try the bottom of Portobello Road market under the Westway white canopy on the corner of Cambridge Gardens every Friday and Saturday.
Friday is the better day, (morning is best), wider range of stuff and a lot of collectors items. Always a number of stalls there on both days with bike jackets, flying jackets or even leather safari jackets (!) and weird stuff, depends what you are after. Old m/cycle barbours even...
Saturday is for the tourists and it gets bloody crowded.
Camden market is worth a look at as well, Saturday and Sunday.
HTH
Charlie