Not much is available ready-to-run, and the Union-TT CC72000 diesel and de Dietrich railcar are quite difficult to find. Even so, there's a good body of material available to model the SNCF of the 1950s.
Steam locomotives
040-D (Jago BR55.25)
050-TA (Jago BR94.5)
150-D (Kittler BR58.10)
150-X (Roco BR44)
150-Y (Tillig BR52)
230-C (Jatt BR38.10)
230-F (Jatt BR38.10)
232-TC (Jatt or MMS BR78.0/T18)
Diesel locomotives
A1AA1A62000 (UMF/www.eaos.pl SM48 or Kemtron RS2 - kitbashed)
CC72000 (Union TT - kit)
Y50100 (Tillig V36 - RTR):

Electric locomotives
CC7000 (BTTB-Start CC7100 - kitbash from 2 shells)
CC7100 (BTTB-Start CC7100 - kitbash from 2 shells)
CC20002 (BTTB-Start CC7100 - kitbash from 2 shells)
Trainsets & railcars
X3700 (Union or s.e.s. De Dietrich):

Passenger & freight cars
A few freight cars have been released over the years in SNCF versions; for others, many of the existing models can be repainted or kitbashed. For passenger cars, in the 1950s and early 1960s - the ideal time period to model the SNCF in TT given locomotive availability - many cars of German design/manufacture were used, and many of these types are available in TT.