Do you have any evidence to substantiate your claims about Chapman’s zebras in the United States, or are you just assuming? There is likely Chapman’s blood in the plains zebra population in the States, but it is extremely unlikely there are any purebred animals left. The plains zebra population is largely hybridized— even many “Grant’s” zebras are to some degree hybrids, though there are far more purebred Grant’s left than there are Burchell’s. The plains zebra population is to be phased out of AZA institutions, single species zebra exhibits are to be replaced with Grevy’s and multi-species exhibits are to be replaced with Hartmann’s. In theory there should be space for another purebred population, but I can pretty much guarantee that will not happen. With the changes coming down the pipeline for SSP and related programs within the AZA, we can really only expect decreases in programs and decreases in species.
Same in Europe, many Plains Zebra are simply hybrids, but not signed as such (in the zoo and on zootierliste). Many animals phenotypically look like the signed subspecies, but there has been a lot of hybridization in the past.