Now you have got me thinking, Nadia! I have this abiding image of a hoe with swan neck prongs; not a 'swan-neck' hoe, which has a blade only. We had one here; we are on the edge of East Anglia, close to Norfolk. I may have to hunt in the outhouses ! It must have had 4 prongs. What is bugging me is that there was such a tool which had a blade on a swan neck fitting on the other side of the shaft, so it was dual -purpose ( you could cut weed seedlings with that side) but I always assumed it was some 'patent' device ( and fairly modern) and an oddity.; what I remember here just had prongs I think. I may have to report back! The Museum of East Anglian Life at Stowmarket (Suffolk) is your likeliest bet , much of it is devoted to agriculture and horticulture, the Norfolk museums or the Royal Horticultural Society may also help you.