Roy died of meningitis at the age of 61 during a visit to Bristol in south-west England in September 1833 and was buried at the city's Arnos Vale Cemetery.
"The ivory bust was the star of the annual event held in memory of the Raja," Carla Contractor, a trustee of the cemetery who organises the commemoration ceremony every September since the 1980s, said yesterday.
"While the main marble statue by sculptor George Clarke has been lost, this is a faithful copy in miniature created by Benjamin Cheverton using a Pantograph machine. It is an amazing find," she said.
The ivory bust belongs to a private collector, who has chosen to remain anonymous but agreed to a request from his art historian friend, David Wilson, to present it for public view at this year's gathering.
The event was attended by hundreds, including the Lord Mayor of Bristol, Councillor Faruk Choudhry.
The bust is considered the best and most accurate three-dimensional likeness of Roy, who was not very keen on having his personal portraits done.