I'm not aware of any manufacturers making them specifically for the bedroom though, for whatever reason?
We got two cheapo's (Usual branded "living area" tent carpet, in a clearance sale). One was just a few inches too big for our 4 berth, and the two together went in our 6 berth... with a very large overlap in the middle (about a third of the bedroom therefore had a double thickness carpet! LOL!)
Just find the nearest size, and fold the edges under if need be.
------------- 2022: 20 nights/4 sites
2021: 30 nights/6 sites
2020: Just 24 nights. :-(
2019: A personal best 50 nights
2018: Just the 30 nights
2017: 34 nights/8 camps
2016: 32 nights/8 camps
2015: 38 nights/11 camps
2014: 34 nights/10 camps
2013: 36 nights
From July 2012: 23 nights
Picnic blankets throughout for me too. Any overlap is just providing a bit of extra insulation. Plus, I have a "runner" up the middle of the tent from the door so I don't have to worry about taking muddy boots off outside in the rain!