Thanks to all who helped in my search for Parker green Quink.
I bought a few bottles from Montgomery Pens in the US. I said I'd post when I received them and I have now.
The ink works really well in my Parker 51 and is perfect for the marking I will need to do for school next year!
Couple of negatives - I didn't receive any correspondance by email from the site, even when I sent in an enquiry. Also, I was hit with a £12 customs charge when the parcel arrived. Watch out if you import something worth more than $30! I didn't mind paying the VAT, but I thought the £8 Royal Mail handling fee was a bit over the top.
Thanks again, the response I got was a really pleasant introduction to this forum.
Mark