The coating is a two part epoxy “paint” and is available in Black, British Racing Green, Stone and Clear. I got it on the web from East Riding Koi (a link to the page is underneath). I ordered it on the Monday and it turned up on the Tuesday, so I cannot fault the delivery.
http://www.koicarp.net/pond_construction/paints_stains/p-1.html
It is probably the biggest expense so far apart from the filters, as I bought two 5 litre tubs which cost in the region of £170, but that was probably similar to a good liner, and the previous 2 ponds have both been liner ponds, and I wanted to do away with all of the folds, especially as this pond is a pretty irregular shape, so putting a liner in would have been a nightmare, and to fibre-glass it would have been a lot more.
You mix it together and add a bit of water and it goes on easily. I have never used it before so we shall see how it performs.