I have a wish to add some abandoned narrow gauge track to my layout. I haven't found anything on here despite searches but have found a mention of handbuilt code 25 rail elsewhere as well as an illusive zz gauge. Can anyone help further. i reiterate it won't be used for moving rolling stock.

If it only for the look, cut down some standard Peco track. A dremmel and a disc cutter would do it.

Look at  the "N Brass"  site , Dummy track, couple of static locos.
http://www.nbrasslocos.co.uk/nline1.html

Easy enough to solder some up. I've done down to 3mm (T) track with PCB sleepers and solder. Even easier if you don't plan to run anything on them.

Code 40 rail is available from various sources including

http://www.britishfinescale.com/category-s/1818.htm

which will also provide you with sprues of chairs with locating pins so all you need to do is to drill suitably spaced holes in plasticard strip or similiar to make the sleepers.

http://www.ntasticshop.co.uk/County-Rolling-Stock-Wooden-Sleepers/dp/B00J0XY2PM?class=quickView&field_availability=-1&field_browse=4380134031&id=County+Rolling+Stock+Wooden+Sleepers&ie=UTF8&refinementHistory=brandtextbin%2Csubjectbin%2Cprice&searchNodeID=4380134031&searchPage=1&searchRank=salesrank&searchSize=12

is another choice on sleepers although you'd need to drill one new hole in each sleeper for the chairs and then cut them down a bit.