So far I have found: a 1-pounder at Anne of Cleves House at Lewes, Sussex; two 24-pounders at Firepower - The Royal Artillery Museum, Woolwich; two or more guns at the Tower of London; a 4-pounder recovered from the wreck of Blackbeard's flagship the Queen Anne's Revenge now at the North Carolina Maritime Museum; a gun that was reclaimed from the wreck of English merchant slave ship the Henrietta Marie now in the collection of the Mel Fisher Maritime Heritage Museum, Key West, Florida.
I have some evidence that there is a Fuller gun at Dover Castle.
Any help in locating cannons made at the Heathfield Forge, Sussex by the Fuller family would be gratefully received.
Many thanks to: Les Smith at Firepower - The Royal Artillery Museum, Woolwich; Nathan Henry, Assistant State Archaeologist and Conservator, Underwater Archaeology Branch North Carolina Office of State Archaeology; Mark Wilde-Ramsing, Project Manager, Queen Anne's Revenge Shipwreck Unit; Friends of Dover Castle

One Pounder Cannon - c. 1749
"The initials IF of the trunnion normally represent John Fuller of Heathfield 1706-1755 but this may be one of the small guns cast by W & G Jukes of Robertsbridge Abbey Furnace. The Jukes[sometimes Jewkes] were commissioned by Fuller to supply him with a number of small iron guns but they forged his initials on the trunnions which led Fuller - a founder of repute - to terminate the contract. The second reinforce bears a shield with a cornet above the letters D probably relating to the first Duke of Dorset, Lionel Cranfield Sackville (1688-1765) who was Variously Lord Lieutenant of Ireland, Constable of Dover Castle and Warden of the Cinque Ports and whose family has long associations with the Weald and Sheffield Park."
Source: Anne of Cleves House Museum, Lewes, East Sussex