Was going through my library again, and found what i was looking for in F.J.G. Ten Raa, 'De Uniformen van de Nederlandsche Zee- en Landmacht hier te lande en in de kolonien' (Van Cleef, The Hage, 1900).
The Garde National is indeed a somewhat eccentric unit type to track down: for example, I didn't know there were 88 cohorts in 1812-1813, and that they were not exclusively linked to either departements, Divisions Militaires or Legions de Gendarmerie (i.e. each territorial unit provided 1 cohort), but were unevenly called up in Military Divisions from the Departments.
For example, in March 1812, in Bruxelles, 24th Military Division, 5 cohorts were called up: 71eme from departements Dyle & Bouches de l'Escaut, 72eme, 73eme and 74eme from Escaut & Jemappes and 75eme from Deux-Nethes & Breda. 71eme is then put into the 147eme de Ligne and the other 4 cohorts into the 148eme de Ligne.
Other Dutch-Belgian cohorts went to the 146eme de Ligne, their compagnies Departmentals went to the 37eme Legere, and according to Ten Raa, remnants and replacements of the 125eme were in January 1813 incorporated into the 134eme de Ligne.
I'm glad I retraced this bit of info, as it gives us Dutch a bit more researchwork to do than just focusing on the well-known (well, in the Netherlands, anyway ;-) 123eme through 126eme de Ligne ;-)
Thanks to all for helping me out,