I've found the R53/56 version from Sparco and few other companies. I swore I've seen a race seat base for the R60 Countryman, but I can't seem to find it.

This is what I found on the Sparco site: https://www.sparcousa.com/product/seat-base-600-series

Do you know where I can find a base plate to install race seats?

For visual please...

(these are the ones I'm installing)

 

Hey sorry to revive an old thread and I'm sure you've already got it figured out but I wanted this to serve as info for other owners putting aftermarket seats in their CM.

I bought these from ebay for my 14 r60. It makes no mention of even fitting a CM so I assumed I would probably have to do some modding/fitting.

Luckily they fit perfectly and I couldn't be happier with em.
Seat brackets