How do I find GenBank records annotated with variation features?

Some GenBank (INSDC) submitters annotate variations on their sequences. You can find such sequence records in the Nucleotide database using this query:
 
variation[Feature key] AND ddbj_embl_genbank[filter] 

If you are focusing on an individual gene, such as human CFTR, you can narrow your search by adding the gene symbol and organism to the search. For example:

CFTR[title]  AND  Homo sapiens[Organism] AND variation[Feature key] AND ddbj_embl_genbank[filter] 

For a human variant of interest, check it against information in the variation databases to see if it is reported by a different submitter elsewhere.