AstroBob.
I'd add Rocky Mountain Caterham to the mix of top Caterham dealers in the U.S.A. Per their website they have sold 8 new Caterhams thus far in 2020 with more on the way. Given that something like 19 Caterhams, total, were sold in the U.S in '19 (per the ongoing R&T article abt their Caterham build), no dealer can make much of a volume claim.
Rather, it seems that Caterham expertise, parts inventory, repair and upgrade services are what separates Beachman and RMC from the rest. I have had significant experience with both and their attention to detail and excellent customer service have allowed Caterham to a visible brand in the USA.
And, I'd add Tom Carlin's Birkin USA into the top 3 se7en resources in the States.
Kitcat:AKA, Sir Spinsalot
'97 Caterham Super Sprint, 1700 Crossflow-sold
'09 Birkin S3, Duratec-sold
'03 Caterham Zetec track car
'19 Honda Type R, sold
'19 Miata Clubsport