Here is a list of suppliers from an old thread of mine with some others 
AdventureStars UK
Akkuteile.de G
AliExpress
All Batteries.co.uk
All Spectrum Electronics US
Anchor Optics US
Ant Supplies UK
Atom Industries.Com US
Arrow.com
BangGood
BatteriesPlus UK
Battery Junction US
Battery Station US
Bushcraft Store
Carlco Optics
Conrad UK
Convoy
CountyComm US
Cousins.UK
CustomLites Inc US
Cutter Electronics US
DH Gate
Digi-Key.com
DTR Laser Shop
DX DealExtreme
EagleTac US
Ecolux
EDC Gear UK
EDCPlus
Elektro Lumens US
EE33 UK
Elite LED.com US
Environmental LED US
Farnell Electronics UK
FastTech
Fenix Store
Flashaholics UK
Flashlight Connection US
FlashLightLens US
FocalPrice
FogStar Batteries
Freshiuk.co.uk Batteries
Future Electronics
HC-Lights
HDS Systems US
Heinnie Haynes UK
HK Equipment
HobbyKing US
Illumination Supply US
Intl-Outdoor Store
Led4power
LED DNA
LED Supermall
LED Supply
LED-Tech.de G
Liberty Flights UK
Light Junction US
Lightmalls
LumaForce US
Lumens Factory
Malkoff Devices US
MindSet Online
Mountain Electronics US
Mouser Electronics UK
NealsGadgets
Nitecore UK
NKON.nl ru.NKON.nl
Odicforce Lasers UK
Optics Planet US
OSH Park PCBs
OSH Stencils
Prometheus Lights
Rapid LED US
ReyLight
RS Components
Sandwich Shoppe
SBFlashlights US
SkilHunt
SkyLumen
SolarForce Sales
SoonDeal
TacLight UK
TaskLED US
ThruNite
TorchDirect UK
UnderWater Kinetics UK
UV Gear UK
Valeno Designs US
Vesture_of_blood US
Virence.com
Wuben
18650 UK
And a couple handy links for modders & builders:
LEDs & Other Stuff
Parametrek.com Flashlight Comparator
LEDCalc - Luminous flux calculator
LEDCalc - Current limiting resistor calculator
SMD Resistor code calculator