Thanks for your thoughts Niranjan, but I'm a photographer first, and a chemist about ninth or tenth. I can follow straightforward chemical recipes for several photographic processes, but cannot create, nor understand chemical workarounds involving substituting, re-calculating etc.. Extra Nitric Acid sounds worrying!!
To Paul - again thanks, great for taking the time to post these links, but these are industrial suppliers and will not supply unless you have business accounts with them, which includes professional chemical storage facilities, minimum orders etc. One of them is only 5 miles down the road from me!! but they still won't!