It's hard to find nightvision manufacturers in the dark forest which is called 'the internet'. So here's a list to help you out. Note that not all manufacturers are selling directly to private parties and/ or selling to international parties without an export license.
United States
Aphotik, LLC
Location: Roswell, Georgia
Products: Designer and manufacturer of low light cameras spanning several sensor technologies and adding intelligence to camera functions.
http://www.aphotik.com/
Aurora Tactical, LLC
Location: Springdale, Arizona
Products: Ground & aviation night vision systems, image intensified and thermal weapons sights, aimers, IR illuminators, thermal viewers, pocket scopes/camera systems, visible and IR laser pointers, IR filters and other night vision related equipment.
http://www.auroratactical.com/
BAE Systems
Location: Lexington, Massachuesettes
Products: Un-cooled IR imaging systems, precision strike EO/IR seeker systems, space subsystems for RF, EO, and digital processing capabilities, high-power microwave systems, ground vehicle situation awareness products, and the conversion of manned combat aircraft to unmanned aerial targets.
http://www.baesystems.com/
CASC-LLC
Location: Salem, Virginia
Products: Consultancy with expertise in electro-optical high technology visioning systems serving businesses in the Aerospace and Defense, Homeland Security and Law Enforcement markets.
http://www.casc-llc.com/
DRS Technologies
Location: Allentown, PA
Products: Ground & aviation night vision systems, weapons sights, aimers, illuminators, IR signaling beacons, thermal viewers, pocket scopes/camera systems, pointers, filters, combat ID devices and other equipment.
http://www.nightvisionsystems.com/
FLIR
Location: Nation wide
Products: Thermal imaging for ground, air, water.
http://www.flir.com/
Hoffman Engineering
Location: Stamford, CT
Products: Image tube and night vision device test equipment and services, photonic test equipment, night vision goggle compatible and covert aircraft lighting and engineered lighting products.
http://www.hoffmanengineering.com/
Insight Technology, Incorporated
Location: Londonderry, New Hampshire
Products: Laser Aiming, Illumination and Rangefinding products, precision location devices; Image Intenification and Thermal Imaging Systems; white light illuminators.
http://www.insightlights.com/
ITT Night Vision
Location: Roanoke, Virginia
Products: High performance image intensifier tubes, night vision goggles, monoculars, weapons sights and long range cameras. Products are designed to meet the requirements of US and international military forces, federal agencies and state/local law enforcement agencies with particular focus on the support of Homeland Security.
http://www.nightvision.com/
L-3
Location: Garland, Texas
Products: Ground and aviation night vision goggles, monoculars, weapons sights, night observation devices, drivers viewers, infrared products, fire control systems and advanced coatings and optics.
http://www.l-3com.com/
Nightline, Incorporated
Location: Mountain City, Tennessee
Products: Full range of image intensification products, surveillance systems and specialty products. Equipment offered is suitable for military/defense application, law enforcement, industrial security and personal safety. GSA distributor for Insight Technology and Northrop Grumman EOS.
http://www.nightline-inc.com/
NIVISYS Industries, LLC
Location: Tempe, Arizona
Products: Thermal, night vision, laser and tactical illumination products for the dismounted operator.
http://www.nivisys.com/
Northop Grumman Laser Systems
Location: Apopka, Florida
Products: Man-portable EO/laser targeting systems, integrated day/night EO sensor systems, laser designators and rangefinders.
http://www.es.northropgrumman.com/
Optex Systems Incorporated
Location: Richardson, Texas
Products: Electronic & mechanical sighting systems, AN/PVS-4 & AN/TVS-5 systems, laser protected glass & plastic periscopes, M36 day/night gunner's periscope and fire control systems.
http://www.optexsys.com/
Photonis USA, Inc.
Location: Sturbridge, Massachusetts
Products: Microchannel plates, advanced performance detectors, channeltrons, flexible fiber optics, custom glass products.
http://http//www.photonis.com/
Raytheon
Location: Dallas, Texas
Products: Advanced thermal weapon sights, driver vision enhancers, and crew served fire control systems. Integrated systems and components designed for high performance in the world's most hostile environs. Products and systems for US and international military forces, federal, state, and local law enforcement agencies.
http://www.raytheon.com/