I don't have much time anymore to keep track of national championships, so for anyone who's interested I'm posting here the 2018 champions that I've collected. Feel free to add and/or correct anything.

Argentina: Federico Villagra - Ford Fiesta MR
Austria: Niki Mayr-Melnhof - Ford Fiesta R5
Belgium: Kris Princen - Skoda Fabia R5
Bulgaria: Miroslav Angelov - Skoda Fabia R5
Croatia: Krisztian Hideg (Hungary) - Skoda Fabia R5
Czech Republic: Jan Kopecky - Skoda Fabia R5
Denmark: Ib Kragh - Citroen DS3 R5
Estonia: Valeriy Gorban (Ukraine) - Mini Countryman JCW WRC
Finland: Eerik Pietarinen - Skoda Fabia R5
France: Yoann Bonato - Citroen C3 R5
Germany: Marijan Griebel - Peugeot 208 T16
Great Britain: Matt Edwards - Ford Fiesta R5
Hungary: Andras Hadik - Ford Fiesta R5
Iceland: Ragnar Bjarni Grondal - Mitsubishi Lancer Evo VI
Ireland (Tarmac): Josh Moffett - Ford Fiesta R5
Italy: Paolo Andreucci - Peugeot 208 T16
Japan: Toshihiro Arai - Subaru WRX STi
Kenya: Carl Tundo - Mitsubishi Lancer Evo X
Latvia: Valeriy Gorban (Ukraine) - Mini Countryman JCW WRC
Lebanon: Roger Feghali - Skoda Fabia R5
Lithuania: Giedrius Notkus - Mitsubishi Lancer Evo IX
Netherlands: Hermen Kobus - Skoda Fabia R5
New Zealand: Hayden Paddon - Hyundai i20 AP4
Northern Ireland: Derek McGarrity - Subaru Impreza S14 WRC 08
Norway: Anders Grondal - Ford Fiesta R5
Paraguay: Gustavo Saba - Skoda Fabia R5
Poland: Grzegorz Grzyb - Skoda Fabia R5
Romania: Simone Tempestini - Citroen DS3 R5
Russia: Sergey Uspenskiy - Subaru WRX STi
Scotland: Andrew Gallacher - Ford Focus RS WRC 01
Serbia: Goran Rabasovic - Citroen C2 R2
Slovakia: Martin Koci - Skoda Fabia R5
Slovenia: Rok Turk - Peugeot 208 T16
South Africa: Guy Botterill - Toyota Etios R2
Sweden: Martin Berglund - Skoda Fabia R5
Switzerland: Ivan Ballinari - Skoda Fabia R5
Uganda: Susan Muwonge - Subaru Impreza WRX STi N12
Ukraine: Borys Gandzha - Mitsubishi Lancer Evo IX
Uruguay: Guzman Rivero - Mitsubishi Lancer Evo X
USA (Rally America): David Brown - Subaru Impreza RS
USA (ARA): David Higgins (UK) - Subaru WRX STi

FIA Africa: Manvir Singh Baryan (Kenya) - Skoda Fabia R5
FIA Asia Pacific: Yuya Sumiyama (Japan) - Skoda Fabia R5
FIA Codasur: Gustavo Saba (Paraguay) - Skoda Fabia R5
FIA Middle East: Nasser Al Attiyah (Qatar) - Ford Fiesta R5
FIA Nacam: Ricardo Trivino (Mexico) - Citroen DS3 R5
Alpe Adria Cup: Michael Kogler (Austria) - Citroen DS3 R3
Euro Trophee: Sebastien Luis (Belgium) - Citroen C2 R2
Mitropa Cup: Gergely Fogasy (Hungary) - Peugeot 208 T16

(need confirmation for these)
China: Gaoxiang Fan - Subaru XV S6
Greece: Ioannis Badounas - Mitsubishi Lancer Evo VI