Many thanks all of you that have replied and helped. A little bit more talking to the local pharmisist assured him and he is getting me half a litre. It is a little less concentrated and will take a bit longer but at least I can try it without having to buy too great a quantity.
Thank you again
PS - I am intending to use a friend's diving resperator and goggles but I won't bother with the flippers!
Got mine via Rydenor. They wouldn't ship it themselves so told me who their supplier was - unfortunately I can't remember who they were! Sorry. I expect if you phoned Rydenor they would probably tell you.
On the subject of safety.....
I used it to fume some oak which worked fantastically. I had a 8 foot table top to do so built a huge chamber out of polythene sheets and cheap 2x1. I put the ammonia in some sandwich boxes out of doors and put the lids on the boxes. After putting the boxes in the 'tent' i sealed it with gaffer tape and using an area where the polythene was lax and popped off the lids. This get up worked very well. When it came time to open the tent i put the lids back on in the same manner, opened all doors and windows and made a small vent in the polythene then evacuated the workshop for 24 hours by which time the vapour had dissipated. Tidy Job.