This is page is updated as I find cool resources for model builders of all skill levels. Model truck, farm models, and parts vendors are represented. 
Disclosure: Some of the links below are affiliate links, meaning, at no additional cost to you, I will earn a commission if you click through and make a purchase.
EBAY sellers and Stores
1981 Gabe Store – DCP trucks
Bossen Implement – Diecast farm and truck models. Wide variety of scales.
Crazy for Green Farm Toys – All sort of 1/64th cars, trucks, farm models
Dairyland Diecast – All sort of 1/64th cars, trucks, farm models
Fleener DCP – DCP truck parts
Hobby Linc – Tons of plastics, brass, glue, everything for great model building.
Highway 39 Diecast – DCP trucks and parts
Mark’s Toy Box – DCP, Speccast, Diorama, Parts
MC2-Toys – Diecast farm and truck. Ertl, Greenlight, DCP, SpecCast
Northwest Die-Cast – Tim Asbury – DCP, 1st Gear, Tonkin, Greenlight
Outback Toy Store – All sorts of Farm and Truck Diecast, plush toys, clothing, branded items
S&J Custom Farm Toys – Farm Toys Trucks and other cool stuff
Model Truck and Farm Model Dealers
Action Farm Toys
Angotti Farm Toys
Big Bear Hobbies and Collectibles
Bossen Implement
Burnett Farm Toys
Canadakotafront float tires , Neo Trucks, KC3 lowboys , TSR, DCP trucks
Custom Build Trucks – Parts
Daltons Farm Toys
Diecast Models Co
DCFarmToys – 1/64 DCP, Winsross, TSR, First Gear trucks
Farm Toys for Fun
HMC Customs
Gottman Toys
Heartland Custom Farm Toys – Custom Farm Toys
M.P. & sons toy trucking – DCP, First Gear, customs, laser cut trailer kits, farm toys.
Mini Truck and Tractor – Standi Toys, Grain bins, dryers, grain legs, hopper bins, hay equipment
Moore’s Farm Toys
Northwest Die-Cast – Tim Asbury – DCP, 1st Gear, Tonkin, GreenLight
Out Back Toys
StampNtoys – DCP, TSR, First Gear trucks, trailers, parts
The LargeCar Model Builder – Resin truck parts and kits.
Toy Tractor Times
Toy Trucks and More – Custom trucks, stainless parts, decals, stock trucks
Tractor Fab
Truckin Little – 1/64 scale stainless and resin parts and cab kits, decals
3D Stores on Shapeways
Cottonwood Farm Models Lee Johnson
Denny’s 3D Classic Trucks and Farm Accessories
Holkerfarm’s Designs
Heartland Custom farm toys by Heartlandcustomfarmtoys
Hamiltons Customs by tyler_hamilton  
JSL Manufacturing by JSLMfg
Cbarfarmtoys by CBarFarmtoys
w_customs by BaileyWiltfang
Doug’s Truck and Farm Models by 877silverado
That Canadian Guy by miniskfarm
Circle C Farm Toys by mcassetty
Mueller Farm Toys by zmueller
Rockin H Farm Toys by RockinH – Shapeways Shops – Grain beds for 1/64 scale trucks, trailers for headers and combines, miscellaneous parts, service beds, manure spreader beds
Lazy F Farm Toys by gmauch
TMattson Farm Toys by tmattson
Dairy scale by James31
RovenModelWorks by RovenModelWorks
Grain Builder by Jay Laudeman
For the Love of Tractors by Jason Shireman
Custom Decals
Bedlam Creations – Custom water slide decals
Circus City Decals – Custom decals and stock
Elm City Toys – Decals is a variety of scales for models.
Graphics on Demand By Christie – Custom peal and stick and stock decals
JB Borth Customs – Peal and stick custom decals and stock decals
Paint Resources
Paint Ref – great resource to find old paint codes
R & E Paint – This outfit can dang near match any color. I have given them some bizarre info and they manage to come up with paint.