Tom,
Start looking on US sites I suggest - I've got some really nice etched HO stuff from Plano for making freightcar brake platforms and walkways. Somebody must do it in 1:48...
Steph
In the US it seems to be known as either 'US Gypsum' or 'Transco' pattern, I guess dependent upon either the manufacturer or installation. It may help your search; e.g. 'Transco roofwalk' or 'Gypsum treadplate'...
You learn something every day Expamet was what I remembered used on the likes of the Cartic 4's and security screening...... No, I'd just have that cigar at your leisure - charities like money!
Model Etch in Adelaide do it in HO, might suit what you need. ME71 is the code, their website is - http://www.modeletch.com/products.html
I have used some of the walkways but not the sheet version.