We can try:
$cmsBlock = $this->blockInterfaceFactory->create();
$copyrightBlock = $cmsBlock->load('copy-right','identifier');
//And then check
if ($copyrightBlock->getId()) {
......
}
Take a look: vendor/magento/module-cms/Setup/InstallData.php
$footerLinksBlock = $this->createPage()->load('footer_links', 'identifier');
[EDIT]
Seem that load method will be deprecated in the future.