The first copies or replicas of the Trinity College harp were the plaster casts, made by (or at least made under the supervision of) Robert Ball of the National Museum in Dublin in the 1840s. I have inspected the one owned by the National Museum of Scotland in Edinburgh, dated 1847; there is also one in Collins Barracks, at the National Museum of Ireland. The Met Museum in New York also used to have one, but it was deaccessioned and sold in the 1980s.
The plaster casts are handsome and impressive, painted to look pretty realistic. They show the harp in a similar shape to its pre-1961 form with a long projecting foot and strange knob at the foot of the pillar. I believe that the cast in the National Museum in Dublin formed the basis for the national emblem of Ireland as seen on the coins, the presidential seal, etc. Read more at my blog.
Cast formerly in the Met Museum, New York. Photo from the 1902 catalogue.
Instrument makers have tried since the 19th century to make working copies of the harp, but the problem there is a lack of good measurements and study of the original, so that copies usually differ in significant ways from the real thing.
Hopefully as more work is done, more measurements and technical data will be published, and we will be able to see really accurate copies of this important historical harp made.