A few early references:
In a description of a witness in a case in "The proceedings at the sessions of peace, oyer and terminer, for the city of London, and county of Middlesex, on Wednesday the 7th, Thursday the 8th, Friday the 9th, Saturday the 10th, and Monday the 12th of December, In the 11th Year of His Majesty's Reign. Being the First sessions in the Mayoralty of the Right Honourable Sir John Barnard, Knight, Lord-Mayor of the City of London. For the Year 1737."
"He told me the Jews name that he had it from, was Solomon Moses, a Fellow with one Eye, that goes about with a Bell-harp."
A description of the Bell Harp in "A musical dictionary; being a collection of terms and characters, as well ancient as modern; including the historical, theoretical, and practical parts of music: As also, an Explanation of some Parts of the Doctrine of the Antients; Interspersed With Remarks on their Method and Practice, and curious Observations on the Phoenomena of Sound Mathematically considered, As it's Relations and Proportions constitute Intervals, And those again Concords and Discords. The whole carefully abstracted from the best authors in the Greek, Latin, Italian, French, and English Languages. By James Grassineau, Gent." Published 1740
An advertisement for one for sale on Saturday, Apr. 14, 1764
Publication: Gazetteer and London Daily Advertiser
Quite a few other mentions in newspapers and monographs around this time.
