The silver was lost for almost two centuries but was discovered by farm labourers in 1827 and returned to the Harris family.
Among the hoard was the so-called Armada Service, a set of 31 Elizabethan silver parcel gilt dishes of varying sizes engraved on the rim with the arms of Sir Christopher Harris.
The dishes were purportedly made from New World silver captured from Spanish treasure ships.
This theory is unproven, but Sir Christopher did work for Sir Walter Raleigh in Devon and Cornwall as an Admiralty official during the clashes with Spain from 1585 to 1604.
Judging by their hallmarks, Sir Christopher is thought to have acquired these dishes with the profits of office between 1581 and 1602.
Some 60 years later, having fallen on hard times, the Harris family were forced to sell the dishes but only 26 were sold, five were missing. The new owners sold the 26 again in 1911 at Christie's for £11,500 and they are now in the British Museum.
But now two of the missing five Armada Service dishes have surfaced and willl be sold by Lawrences of Crewkerne on October 15.
The 8in (20cm) diameter dishes are hallmarked London 1601 and estimated at £50,000-70,000 for the pair.
Lawrences silver specialist, Alex Butcher, said: "It is still a mystery why these dishes were separated from the original set of 31."
The vendor believes that they were purchased in an estate sale somewhere in the Southern states of America.
"It would be great to reunite them with the other dishes and be fantastic if the missing three should come to light."
He added: "It's extremely rare that any domestic plate made before 1640 survives. It was almost all melted down during the Civil War."
Contact Lawrences on 01460 73041.
By Anna Brady