Regardless of distribution channels, if it's warranty coverage, I'd say it has to be HPI.
This is what is currently on the HPI website:
To ask a question in the US, please contact support by email [email protected] or call our service center on (217) 398-0007.
It's actually HRP and A Main in North America.
Here's the official press release from HPI:
http://www.liverc.com/news/announcements/16400-HRP%2C_A_Main_Hobbies%2C_and_Hi-Performance_appointed_as_new_HPI_Racing_North_American_distributors/