Small rant from an event breeder…
I would start in the US. Just because it is bred elsewhere doesn’t automatically make it better. There ARE breeders in the US who produce event horses and nice ones at that. AND, you support the people who are the backbone of the sport - without them, you won’t have young horses to ride.
Off the top of my head, I would say here in Area 2, Phyllis Dawson, Wits End Eventing ( although they may be area 3), Clear Blue Farm- Laurie Cameron in NJ, Kurt Martin has a lot of young horses , although mostly imports, Courtney Cooper knows where to look for some and has nice ones come through there, Bruce Davidson, Melissa Studenberg of Kealani Farm- are just a few.
Ask some of the upper level riders that actually ride young horses where they get theirs - Doug Payne is a perfect example of bringing up youngsters from backing to advanced. He gets them from the US.
Outside of Area 2, Megan Moore of CEO Eventing in KY always has nice horses. Try looking at the Facebook group Event Horse Breeding in North America - you will find out that many of the successful event bloodlines that are worldwide can be found in your backyard
Sorry, rant over…