OR-Library is a collection of test data sets for a variety of OR problems.
A full list of the test data sets available in OR-Library can be found here.
There are 30 test problems.
These test problems are the test problems involving 100 and 300 nodes as in Table 6 of the paper Fleurent C. and Ferland J.A. (1996) Genetic and hybrid algorithms for graph coloring, Annals of Opns Res. 63, 437-461.
These test problems are gcol1, gcol2, ..., gcol30
These test problems are in DIMACS format (e.g. see here for a link to a description of that format) and have been contributed by Dr Bill Dowsland (firstname.lastname@example.org)
Click here to access these files
OTHER SOURCES A variety of test problems are available from DIMACS, via anonymous ftp here (see also here)
Test problems are also available here and here