Can someone help, I am looking for chapter wise MCQ set (around 200-300 questions) for all GS prelims & mains subjects (History, Geography, Polity etc.)?

Well you can try the following initiative:

KSG 10,000 which contains some 10k questions, relevant in my view. Fill the form and you will get the link to download the pdf.

https://www.ksgindia.com/10000.html

Also Insights provides a set of books(Question Bank) ,divided subject wise, which are available on Flipkart & Amazon (provided you're in Orange, Green Zone for delivery).

Edit : Forum IAS has provided free pdfs of SFG Tests of both batch. They will surely quench your thirst.You can download them via telegram.

Telegram Links are forbidden here !! Now lets see if forumias will make an exception :P

In that case you paste the link inthisgoogle sheet. :p 

Thanks@Osho, @Naadan_Parinda &@goldberry