Since I am admin I am adding all TCR championship on site I will try to answer this.
1. Ford Focus
If we count all three versions of Focus (
http://www.webcarstory.com/voiture.php?id=20309,
http://www.webcarstory.com/voiture.php?id=21878 and
http://www.webcarstory.com/voiture.php?id=24090). There are at least
two cars.
2. Honda Civic
Prince Racing was running 2 cars in 2015 TCR Asia and I think they are sold now to other TCR Asia Teams
WestCoast Racing have 5 cars (15/16 Morbidelli), (15 Gleason/16 lot of drivers), (15 Munnich/Skuz/Rakhmatulin/Wong/16 Pellinen/Grachev), Huff car in 2015 Macau and new car for Morbidelli for Singapore)
Henry Ho have his own Civic
There are 4 cars in Thailand run by 1xVattana, 2x TBN MK Ihere and 1xEakie
There are 2 cars in Benelux run buy Boutsen Ginion and there was guest car in special livery
Rikli have 2 cars for ETCC as well as Munnich have 1
Target have 3 cars for TCR Germany (one was driven by Jordi Oriola in TCR International
There are 2 cars in TCR Germany for ADAC Honda Team
And Finlay Crocker have 1 car he used in Germany and Italy
Roberto Colciago have 1 car for TCR Italy along Emanuele Alborghetti
Jose Rodriguez drive 1 car in TCR Portugal
So there are
26 Civics
3. Kia Cee'd
There are at least
1 test car
4. Opel Astra
There are 2 VLN spec cars driven In 2015 season
For new Astra
There are 2 'factory' cars. 1 raced in TCR Benelux and TCR Germany by Corthals and will be used in Singapore by Oriola
and second used by Oriola in TCR Germany
One is used by Lubner Motorsport in TCR Germany
One car raced by Moura Laser in TCR Portugal
And two raced by Traget in Bahrain (maybe they are same car as those two factory cars)
Old+New Astra there are
6 or 8 cars
5. Renault Megane
1 car is used by Ralf-Car in TCR Russia
6. Alfa Romeo Giulietta
There are 2 cars run by Mulsanne Racing
1 car will be run in TCR Benelux by Charleroi on Tracks
and 1 will be driven in ETCC by Team Unicorse
So
4 Alfa's
7. SEAT Leon (TCR spec)
1 car is driven by Douglas Khoo in TCR Asia
There are 3 cars used in TCR Benelux
There are 8 cars in ETCC (2xKrenek, 1xZengo, 1xSpeedy, 2xLein Racing, 1xJSB, 1xPfister)
There are 9 cars in TCR Germany (1xHP, 2xLMS, 1xBas Koeten, 1xSteibel, 1xWolf-Power, 1xTOPCAR, 2xTarget??? MAybe Target have more Leons)
There are 6-7 cars in TCR Italy (3xBRC, 1xPit Lane, 1xEsse, 1xMM, 1xTecnodom (maybe Tecnodom was sold to some other team)
There are 4 in TCR Portugal
There are 7 in TCR Russia
I don't know how many TCR's are in TRC Spain
There are 7 in TCR International (3xCraft-Bamboo, 3x B3 Racing, 1x BD Racing) Also Buri and Laaksonen used cars from TCR Germany, Mora used car from TCR Portugal and Hezemans used his own car raced in TCR Benelux
There are at least
45-46 TCR Leon's
8. Subaru WRX STi
There are
2 cars
One raced in 2015 and at the start of 2016. Coming back at Singapore
And other raced from Buriram 2016
9. Volkswagen Golf GTI
Engstler have 7 cars (2 are racing in TCR Asia, 3 in TCR Germany and 2 in TCR International 2015/16) *Conrad/Mackschin car was raced by Gary Sheehan in TCR International
There are 2 cars raced by Teamwork and 1 by Song Veng in TCR Asia
There are 5 in TCR Benelux (2x Delahaye, 2x Milo, 1xWRT)
There are 2 in TCR Germany (1xRacing One, 1xJBR)
There is 1 in TCR Portugal raced by Novadriver
There are 2-3 cars in TCR International (All by WRT, maybe Buri car is car from TCR Benelux)
So we have
20-21 VW Golf
10. Peugeot 308 TCR
Since Peugeot appeared on TCR car list there are at least
2 cars raced in TCR International and ETCC
If all this is correct there are
109-113 TCR cars build