This page is a random collection of suppliers I found while googling for various P38 bits.
I must stress i have not so far purchased from most of them and I am not making any recommendations.
I built this page for my own convenience, but I hope it helps others as well.
I have just added a section on Aussie Fabricators July 2013

Land Rover online Parts Site Invaluable resource

MicroCat for Land Rover online To find any part number, invaluable resource

MicroCat for Land Rover online Just navigate to the English section to find any part number, invaluable resource

Australian Fabricators

There is a small but growing number of companies filling the gap and fabricating Bars, Sliders etc for the P38.
I shall attempt to keep this list current. The current major missing piece is a snorkel !

Rijidig Offroad Murray provides all the bits you need to make a wheel and or Jerry can holder

APT Fabrications Currently make a Winch Bar and Sliders possibly diff guards as well. Rear Bar due in September 2013

Brahma Bar Not sure if this is still available

MCC FALCON BAR MCC707- 02, These bars fit the P38 and support ADR

Outback Accessories Australia XROX Winch Bar

ECB The Disco Bar may have been adapted to fit

S and J HorsePower A Disco 2 Bar has been adapted to fit

TradesMan Roof Racks Make a great rack which uses the factory mount points

RockSliders Are happy to make P38 silders if they can get a vehicle in Brisbane to use as a template

4B Fabrications Have fabricated a custom stainless steel snorkel for a P38

LAB Electronics BECM and Key Reprogramming Service

Range Rover Solutions Russell sells Brake Modulator rebuild / upgrade kits

Aussie Desert Coolers Fabricate high quality all aluminium radiators for Range Rovers

Range Rover BECM Test and Repair Can test and repair the BECM and much more

United Kingdom

Landrover Workshop Community Parts DB
This site allows to compare prices across a few suppliers
and has some helpful hints on which parts to buy

LR Direct Reputable supplier I have used

Paddock Spares Reputable supplier I have used

Island 4x4 Reputable supplier I have used

Brit Car Reputable supplier I have used

LR Centre Reputable supplier

L.R. Series

John Richards Surplus

Brit Part

British Parts

P38 Spares

DLS

Hobson Land Rover Parts

British Parts

Range Rover Parts Store

Famous Four

John Craddock

Terrain 4x4

Landy Boys

LR Spares

Southdown 4x4

DingoCroft

Landy Parts

4x4 Parts UK, lots of bearmach stuff

 United States

Landrover Parts Cheap

Global British

Atlantic British

Voyager RacksRear Laddder for P38

 Australia

RoverLord Offroad Spares Reputable Australian Mail Order business

Grahame Cooper Sydney, NSW

Triumph Rover Spares Adelaide, SA

Les Richards Automotive Melbourne, VIC

T.R. Spares

Land Vehicle Spares

Rover Parts

KarCraft

4 Wheel Drive

All 4x4

Central Coast 4x4 Wreckers

British Parts

AJG Spares

Range Rover Wreckers

British Offroad

Rova Craft

TradesMan Roof Racks

Rijidig Offroad

APT Fabrications Winch Bar, Rear Bar and Sliders

Brahma Bar Not sure if this is still available

MCC FALCON BAR MCC707- 02

Outback Accessories AustraliaXROX Winch Bar

ECB

S and J HorsePower