MODEL RAILWAY GROUPS ON FACEBOOK (Selection only, updated 15th November, 2017.)
Rough order by title; numerical, then letter, then A to Z
Open this page on a new tab after you've signed into Facebook.

COLUMNS (If empty, I'm not sure.)
TYPE = "public" = you can look without joining; "closed" = you have to join to read the contents.
SCALE = self-explanatory; but "brand" = covers all gauges produced by the maker.
MAP = the group owner has filled in the location option.
HELP = indicates the group members will help you out on queries.

00 and N gauge. Trains and layouts. closed 00, N   yes yes yes
HO and N scale Model Trains Buy Swap And Sell All Kinds closed H0, N yes   yes  
TT-Modellbahnfans und Freunde Tauschbörse closed TT yes   translator  
Z Scale Model Railroading Enthusiasts public Z no   yes yes
Anything TRAINS Australia - Buy Swap Sell public all yes yes yes yes
Australian N Scale public N   yes yes yes
Anything OO Gauge closed 00     yes  
British Railway Modelling In Australia public all   yes yes yes
Buy/Sell Z Scale Model Trains and Equipment closed Z yes   yes  
Dinky Toys and Hornby Trains For Sale and Wanted public brand yes   yes yes
Dublo, Tri-ang & Hornby Buy & Sell public brand yes   yes yes
Early Mantua/Tyco Collectors Group closed H0 yes   yes yes
Hornby Dublo Enthusiasts public 00, H0 no   yes yes
Hornby 0 Gauge Trains - HRCA closed       yes public Z, H0 no yes yes yes
Micro Layouts closed       yes  
Micro/Small Model RR Layouts closed all no   yes yes
Model Railways Buy Sell Have Fun. closed all yes yes yes yes
Model Railway Buy Swap Sell QLD public all yes   yes yes
Model railway enthusiasts public       yes  
Model Railway Stuff - Buy, Sell and Exchange public       yes  
Model Railways closed     yes yes  
Modeling Desert Scenery public       yes  
NSWGR Steam Era Modelling closed all     yes yes
Railway Fans Blue Mountains NSW (my group) public all yes yes yes  
Southern Pacific Modelers closed       yes  
Triang Railways Collectors closed brand     yes yes
TT3 Model Train Fans (my group) public TT yes yes yes yes
Vintage Model Trains public all yes   yes yes

Corrections and additions to John .

TRI-ANG RAILWAYS Australia main page

Photo at the top, 2017, the large H0 layout belonging to a member of Valley Heights Museum.