Halfway down this webpage you can find most of these, under the heading "common epitope tags".

https://www.addgene.org/mol-bio-reference/genetic-code/

Emily, James asked for the antibody sequences, not the tag sequences.

There may be multiple antibodies in use for the same tag, both monolonal and affinity-purified polyclonal.

James: You would need the name of the specific antibody whose sequence you are looking for, as there may be multiple monoclonals around that recognize the same tag. You may be successful searching GenBank (https://www.ncbi.nlm.nih.gov/genbank/) for that name. However, commercial antibody sequences frequently do not get deposited in the databases.

We published the sequence of anti-C-terminal His-tag antibody 4D5 together with stabilizing mutations and the structure of its complex with an olig_His peptide in https://www.bioc.uzh.ch/plueckthun/pdf/APpub0220.pdf, pdb entry 1KTR.

For the anti-flag M2 antibody, a structure of the complex is also available in the PDB, therefore you can get the sequence from pdb entry 2g6 Article Structure of anti-FLAG M2 Fab domain and its use in the stab...

These are amino acid sequences, but you may search the nucleotide databases with these to find the original nucleotide sequences, or just reverse-translate to generate

Annemaria - thank you very much. That is what I was having difficulty finding.