Free Advice!
Before you spend a fortune on a "rare" vintage Honda part on ebay, check with your local Honda dealer and the suppliers listed below. It's amazing what Honda still has in stock. I often see used items on ebay going for way more than you'd pay for new. I've done it myself more than once.

The links below are designed to bring you as directly as possible to the relevant parts page on the site.

CLassic Motorcycle Supplies - Located in Holland. Incredible well organized collection of Vintage NOS Honda Parts. Prices are in Euros! They ship worldwide.

Bike Bandit OEM Parts - Online Schematics - Parts Lists

PartsNMore.com -- Great source for non-OEM parts for the Hondas listed below
CB/CL360
CB400
CB650 SOHC
CB650 DOHC
CB750 SOHC
Magna/Sabre/Interceptor
VF1000
Magna/Sabre V65 VF1100
CB750/900/1100 DOHC
CBX
GL1000/GL1100
GL1200

NOS (New Old Stock) Vintage Honda Parts

Western Hills Honda -lots of NOS parts

David Silver Spares_NOS Parts - in UK
Prices are in British Pounds!

Reproduction Parts

David Silver Spares_Pattern(Reproduction) Parts
Prices are in British Pounds!

ZPower Austalia -
Some Interesting (not cheap) Reproduction Parts for CB750s
Seat covers, side covers, badges, decals etc.

Z50, CT70, QA50, SL70 Parts -
Northeast Vintage Cycle, loads of NOS and aftermarket parts for these little beauties.

And Obviously ebay
This link will list all Honda parts on ebay between 1950 and 1980. Once you get there, refine your search using the column on the left.

Decals

reproductiondecals.com
Reproduction Decals for vintage motorcycles

Keys

http://www.hondakeys.com/
Original NOS Honda keys

Fasteners

Rimfire Engineering CycleScrews
OEM Replacement Fasteners for the Vintage Motorcycles

Tires

KG Motorcycle Tires & Accessories
Tire Size and Battery Chart

High Performance Vintage Brakes
VintageBrake.com

CB750 Parts fromJapan - Amazing selection of 750 parts
www.yamiya750