Bill,
From the IGC:
There was a Gilbert Forbes in NY at 18 Broadway.
An advertisement appeared in the New York Journal and the General Advertiser on 16 March 1775 saying, 'Gilbert Forbes, Gun Maker. At the Sign of the Sportsman in the Broad Way, opposite Hull's Tavern in New York. Makes and sells all sorts of guns, in the neatest and best manner; on the lowest terms; has for sale, Silver and Brass Mounted Pistols; Rifle barrel Guns, Double swivel and double roller gun locks; 50 ready mad new bayonet guns, on all one size and pattern'. He made many rifles and muskets for Governor Tryon. He got involved in the Hickey Plot to kill or capture General Washington. When the plot was uncovered, many of the conspirators were taken, amongst them Forbes and Hickey. Forbes turned state's evidence and the result of which was the public hanging of Hickey in mid 1776. This making Forbes very unpopular resulted in Forbes fleeing the city and vanishing without a trace.
Pete