There is a Yahoo Group devoted to Egan harps, which is a good place to ask this question. Link is
http://launch.groups.yahoo.com/group/johneganharps/?yguid=327814981
The Egan I have personal experience of (a Grecian, hence not a single-action, made in 1835) had the maker’s current address engraved on the forepillar, which was 30 Dawson Street, Dublin.
I also have the following list (though I don’t quite understand the repetitions and date-sequences, nor whether the “harp & piano maker” in Bride Street is also Egan).
HARP MAKERS IN IRELAND – From the Galpin Society Journal, May 1963
JOHN EGAN Pedal and Portable Harp Maker to His Majesty
25 Dawson St Dublin, 1804-1810
30 Dawson St Dublin, 1821
30 Dawson St Dublin, 1830-1831
23 Dawson St Dublin, 1832
30 Dawson St Dublin, 1833-35
Harp and Piano Maker
57 Bride St [Dublin]
26 Dawson St, 1838
44 Dawson St, 1841
EGAN, READ & TAYLOR
21 Aungier St [Dublin], 1821
FRANCIS HEWSON, Harp Maker
19 South King Street [Dublin], 1830
WILLIAM JACKSON Pedal Harp Maker
38 Grafton St [Dublin], 1834-1835
7 Molesworth St [Dublin], 1838
JOHN READ Harp Maker
28 French St [Dublin?], 1837-1839
NICHOLAS READ
21 Aungier St, 1833-1835
4 Peters Row [Dublin?], 1833