This page is a collection of suppliers of parts, equipment, and materials for camper van conversions. 

I'm not endorsing any of these suppliers -- I don't have any first hand knowledge of most of them -- its just a place to start looking. I don't have any financial or other connection with any of them.

EuroCampers

EuroCampers.com

EuroCampers has a wide variety of parts and equipment useful in a van conversion.  

Some custom fit stuff for Sprinter, Transit and ProMaster.

Camping World

Camping World

Well known chain offering a large collection of RV and camper conversion parts.

Retail stores in large cities.

Amazon

Amazon

 Amazon has a surprising amount of specialized hardware and equipment for camper van conversions.

ProMaster World

ProMaster World

Stuff for ProMasters:  Running boards, Shelving, Windows, Hitches, Lighting...

Plastic Mart

Plastic Mart

A major supplier of plastic tanks for fresh, grey and black water systems on RVs.

Best Converter -- RV Electrical Supplies

Best Converter

Wide variety of RV and camper van electrical gear.

Inverters, converters, distribution panels, gauges, solar, lights, water heaters, ...

Surplus Online -- pats and accessories for RVs

Surplus Online

Wide variety of RV and camper conversions gear.

Appliances, vents, AC, electrical, mattresses, shades, tanks, toilets, seating, ...

RV Teardrop Trailer Parts, Kits, Custom Built Trailers

Vintage Technologies -- Teardrop Trailer kits and parts

Interesting site with a wide variety of hardware to make teardrop trailers -- much of it also useful for other conversions.

PPL RV Parts and Accessories

PPL RV Parts and Accessories

Wide variety of hardware useful in camper conversions.

AC, awnings, electrical, furnaces, lights, plumbing, fridges, solar, stoves, hitches, vents, water heaters, ...

Panther RV Products 

Panther RV Products

A variety of hardware useful in camper conversions.

An ebay store.

Impact Products 

Impact Products

Hein's company provides a number of specialty products for converting vans to RVs.

Hein is a frequent poster on the Sprinter, Transit and ProMaster forums, and as done a number of very nice van conversions.