There's nothing unknown about the Echinades: here they are and see O.U.p.264 for the location map. There is a useful discussion about them at http://en.wikipedia.org/wiki/Echinades
which indicates that there are 17 named Echinades today but there were many more historically before alluvial deposits from the Achelous river connected them with the mainland, as described at O.U.p.265.
The article also states that some of these islands were still claimed by today's island of Ithaki in recent years, and another entry states that Makri (at the centre of the photograph) is today administered by the municipality of Ithaca.
The fact that Meges leads "Men from Doulichion and the sacred isles of Echinai" at Il. 2.625 may therefore explain why they provided 40 ships against Ithaca's 12, since almost every resident of such small islands would need to be a sailor.
It may also explain why 52 suitors against Ithaca's 12 are identified with Doulichion at Od. 16.245. Suitors from the Echinades are not listed elsewhere so this total must include them and each island would probably have provided at least one suitor.
Furthermore since several of these islands have now become joined to the mainland, part of today's rich agricultural coastal land then formed islands governed by Doulichion, supporting the poet's "rich in wheat" description (see list of clues on p.270).