I know about an antibody of My BioSource, one that binds the E1B 19KDa protein.
This is the link: https://www.mybiosource.com/recombinant-protein/e1b-protein-small-t-antigen-e1b/1199669
Sigma-Aldrich offers an antibody that binds the proteins expressed by the BNIP3L-gene. These aren't antibodies against the Ad5-E1B-19KDa protein, however, but against the Adenovirus E1B19K-binding protein. This is the link: https://www.sigmaaldrich.com/catalog/product/sigma/hpa015652