When purchasing a valve kit, particularly from overseas, check the shipping costs carefully. It is not unusual for a pair of monoblock valve power amp kits to weigh 20-30kg and the freight costs can be considerable. It's also advisable to insure any major purchase and ship by courier rather than the regular postal service.
Audio Electronic Supply 
Audio Note (U.K.) 
Audiophile (local distributors for Audio Electronic Supply) 
Borbely Audio
Bottlehead Corp
Curcio Audio Engineering 
Hawk Audio
High Fidelity Engineering (Decware) 
DIY
Hi-Fi Supply 
Mapletree Audio Design
Oatley Electronics
Quality Kits (distributes Velleman
valve kits) 
Sun Audio
Transcendent Sound
Vacuum State Electronics
Valve
Electronics 
Vintage
Hi-Fi
Welborne Labs
World Audio Design