You asked whether a reproduction of the portrait of Sir John Pettus, mayor of Norwich in 1608, is available. I have not seen one in a museum shop, but the portrait was used to illustrate a glossy book on Norwich published not many years ago. I have a copy of the book that someone sent me a few years ago, but it is not presently accessible (we are in the midst of painting and replacing the carpets). I don't remember the title, but the author's name, Pound, just came to me. You might try searching under his name at an on-line bookstore.
I also plan to use Sir John's portrait as an illustration for a book I am writing on the Pettus family. I don't have a publication date yet, but I have written a first draft and am now getting permissions to quote from copyrighted materials and to use certain pictures as illustrations. This is a rather time-consuming process.
According to a correspondent who visited Norwich within the last few years, the church is kept locked, but the key is available from the deanery at the Cathedral.
Thomas Petyous who was established in Norwich in 1492 supposedly was buried in St. Edmund the King Church on Lombard St. in London (death or burial date unknown), but the old church was destroyed during the Great Fire of London in 1666. The present church at that same location was (I think) designed by Chrisopher Wren. The church was locked when I made a visit, and I never got a reply when I wrote a letter of inquiry to see if the tomb of Thomas Pettus (ca. 1500) was still extant.