June 2019
Is there any way to get it nowadays or is it just permanently gone and cannot be attained?
June 2019 - last edited June 2019
The only version where the Challenge Series is working is the EA DVD version with patch 1.0.1.18 installed. You can still find copies for sale at online retailers. If you don't play online, a used copy should be good enough. You can do a web search for patch 1.0.1.18 to download and install it. The EA Store download version also worked, but it's no longer available, and the Challenge Series doesn't work in the Origin download version.
The Challenge Series is unlocked as soon as you do the career mode prologue, which allows you to run the Challenge Series and win three tier 1 cars which you can then use at the start of career, even though it normally starts with tier 4 cars.