There should be no washer between the cone locknut and the dropout. The anti-rotation washers go between the axle nut and the dropout with the tab(s) in the slot. There will be a cone-fixing washer between the cone and locknut on the drive side and maybe a spacer washer between the non-drive side cone and lock nut.
A few more posts for you and you can upload some pictures, which will be very helpful.
SJS Cycles in UK is my main source of SA spares. They have a variety of anti-rotation washers. The key dimensions are the thickness and slot width (usually 9.5mm).