Whilst the main focus of this Hub is on UK stock and manufacturers, TT120 has been established for years in mainland Europe, especially in Eastern Europe.
From the Hornby forums, Ilmson very kindly produced the following comprehensive list, which I am copying below. Most of these companies I am not personally familiar with, but they certainly offer a useful additional field of interest for UK TT120 modellers.
Scale 1:120 standard gauge
Tillig - freight wagons and other Central European wagons; Central European locomotives, TT rail systems
Roco - freight wagons and other Central European wagons; Central European locomotives, TT rail systems
Piko - freight wagons and other Central European wagons; Central European locomotives
Igra - freight wagons and other Central European wagons; Central European locomotives; Lasercut (pre-colored): buildings, bridges, decoration
Sudexpress - freight locomotives, freight wagons (still under construction)
NPE - freight wagons
SDV Model - freight wagons and other Czech wagons;
Peresvet - freight wagons and other Central European and Russian wagons;
Loco - Czech freight wagons and passenger wagons;
MTB - Central European locomotives; American locomotives
Busch - freight wagons and other Central European wagons; Accessories (injection molding + lasercut): buildings, decoration, figures, vehicles; Lighting (with LED)
Auhagen - injection molded plastic: buildings, bridges, decorations, figures, vehicles;
Vollmer - injection molded plastic: buildings
Hädl - freight cars and other Central European cars
Kres (Fischer-modell) - German railcars and double-decker trains
Gützold (Fischer-Modell) - German steam locomotives
Saxonia - aging of models; German steam locomotives; laser cut: buildings
Schirmer - German steam locomotives
BeckmannTT - German locomotives
Panzer-shop.nl - 3D printing: vehicles, figures, animals, decorations
Modellbahn Union - seller with self-made accessories: buildings, vehicles, figures, animals, decorations
Viessmann - lighting (with LED), German signals; Overhead wires
Sommerfeldt - Overhead wires
KB-MODELL - Lasercut: buildings, bridges, decoration
MKB-Modelle - Lasercut (pre-colored): buildings, bridges, decoration
JM-Detail - Lighting (with LED); LaserCut: buildings, bridges, decoration
MBZ model railway accessories - Lasercut (without color): buildings, equipment
Atelier Wepe - Lasercut; buildings, decoration
Jako Models - Lasercut: buildings, bridges; 3D printing: decoration
Laffont - Lasercut: buildings
TT-Koch - Vehicles (transport, agriculture)
Minatur - Vehicles; Decoration
Weinert - Lasercut+ etching technology: Decoration
Artitec - Resin cast: Figures, vehicles, boats, decoration
Radestra - Resin cast: Buildings
Herpa - Vehicles
VV-Model - Vehicles
Noch - Figures, decoration
Preiser (+Mertens) - Figures
ES-Pecky - Decoration
Veramo - Decoration
Model Scene - Decoration
MBR Model - high-quality trees and bushes in TT
Polak - grit; meadows, bushes; various ballast in TT grain size: porphyry, melafyr, gneiss, granite, phonolite
Digital-Zentrale - accessories, track cleaning, cleaning vehicles
Lux-Modell - cleaning vehicles
Hack - bridges
Voigtländer/Stromlinie - resin and etching kits: German wagons and locomotives
Scale 1:125
Diecast Masters - construction site vehicles, open-cast mining vehicles