I am trying to find the best source(s) for parts for a 2003 Defender. First up are oil and air filters, fuel filters (engine compartment and rear frame mounted) and a fuel filler cap (gas cap). The vehicle came into my possession and is getting some much needed, but belated TLC.

 

Where have you looked so far?
Might want to try Rover's North.

 

RovahFarm - Parts for Land Rover Cars and Accessories - Land Rover Discovery, Range Rover, LR3, LR2, Land Rover Defender, Freelander and Land Rover Series

 

Rock Auto and CarPartsDiscount have good prices for general maintenance items, but don't expect to find anything too specialized.