The Nucleotide database contains mitochondrial genome records, including those from human genealogy studies. To retrieve all human mitochondrial genome sequences use the following query to search the database:
human[organism] AND mitochondrion[title] AND genome[title]

Haplotype or haplogroup information will be available only if provided by the submitters of the records. To find those records that have the haplogroup or haplotype information use the following:
human[organism] AND mitochondrion[ti] AND complete genome[ti] AND ("src haplogroup"[Properties] OR "src haplotype"[Properties])

Make sure to use parentheses when you combine two search terms with the "OR" Boolean operator. The "src" abbreviation stands for source modifier and haplogroup and haplotype are two source modifiers from GenBank's controlled vocabulary.

If you are interested in other types of human variation, explore several NCBI services dedicated to medical genetics and human variation.