Manutti
Furniture (Contract/Commercial)
Roberti
Outdoor furniture.
Cassina
Talenti
All outdoor, they even have outdoor kitchens
Poliform
MINOTTI
Upscale Italian brand.
New Design Group
Formetiq
HILLE
Classroom Chairs | School Chairs | Stacking Chairs
Vepa Furniture
Race Furniture
Theatre/venue seating
Deadgood
Zioxi
Wiesner-Hager
James Burleigh
Flexiform Business Furniture
Orangebox
Gresham Office Furniture
S•CAB
Pretty outdoor furniture and lightweight metal interior and work furniture
Fenabel
Perfix
lockers, filing, towers and storage cabinets
Ghidini 1961 | Contemporary Italian Furniture
MaxAlto
Metadil Store
Southwest Solutions
Cider
Halle+
Industry West
Blu Dot
Not sure if this is contract grade furniture, but I signed up for a trade account and 3D files and spec sheets are available.
COR
I've used many of their lounge seats, including "Shrimp" and Nenou. They provide downloads here: https://www.cor.de/en/downloads (and on BIMObjects)