I don't understand why people recommend searching Google Scholar or Mathscinet. Just try typing
Chun and Seymour (1989)
in Google. There are no obvious hits. But since it is supposed to be about graph theory, try typing this into Google:
Chun and Seymour (1989) graph theory
and the fourth hit is
Handbook of Graph Theory, Second Edition
Jonathan L. Gross, Jay Yellen, Ping Zhang - 2013 - Mathematics
[ChSe89] F. R. K. Chung and P. D. Seymour, Graphs with small bandwidth and cutwidth, Discrete Mathematics 75 (1989), 113G119. ... Chung and W. T Trotter, Jr., Triangle—free graphs with restricted bandwidth, Progress in Graph Theory, ...
so it looks like you should look for this:
F. R. K. Chung and P. D. Seymour, Graphs with small bandwidth and cutwidth, Discrete Mathematics 75 (1989)
googling which yields this pdf as the first result.