By.cssSelector("<tag>[<attribute>='<value>']")

List<WebElement> elements = driver.findElements(By.cssSelector("select[ng-model='income.frequency']"));

List<Select> selectList = new ArrayList<>();
List<WebElement> elements = driver.findElements(By.cssSelector("select[ng-model='income.frequency']"));
for(WebElement element : elements) {
    selectList.add(new Select(element);
}