Tracking down myths
Here is fuller information on sources for Greek and Roman myths:
Roscher = Ausfuerliches Lexicon der griechischen und roemischen Mythologie (multiple volumes, starting in 1884-)
Preller-Robert = Griechische Mythologie (4th edition 1894, Robert's revision)
LIMC = Lexicon iconographicum mythologiae classicae (multiple volumes)
Another work that is sometimes useful is
StithThompson = Motif-Index of Folk-Literature (6 vols.).
There is a copy of Roscher in the CNES library. LIMC can be found in Wilson Library reference. I don't think that the University owns a copy of Preller-Robert, but there are copies of Preller's unrevised Griechische Mythologie and Roemische Mythologie (in the CNES library and also in the Wilson annex, where a number of older things is kept--if you go for them in person, you'll have to do it during the day when they're open.) Stith Thompson is also available in Wilson reference.
The other work we discussed, not necessary as useful for Vergilian scholarship as for other things (like teaching a myth class) is
Reid, J. D. The Oxford Guide to Classical Mythology in the Arts, 1300-1900s (Oxford 1993). This is a 2 volume work. There is a copy next to Roscher in the CNES library.