I hadn't heard of this paper, and I use Ilford a fair amount. It's not obvious whether it's still readily available, given the final bankruptcy of Ilford Imaging in Dec 2013 after a series of near bankruptcies, and the subsequent purchase of the trademarks and associated assets by Chugai Photo Chemical Co. Ltd of Tokyo, Japan and C.R. Kennedy & Company Pty Ltd of Melbourne, Australia in May 2014. (Note: the portion of Ilford that makes traditional film and paper, which is now a separate company located in the UK and not Switzerland, was unaffected.)
There is a little info about this paper in this thread:
My experience is that you can use the Gold Fibre Silk piezo curves for papers like Galerie Smooth Pearl and Gloss. I printed the 21x4 chart and measured linearisation for these papers and the similarity to GFS was uncanny. Piezo prints using the GFS curves are fine. It's my impression that a lot of these Ilford gloss or semi-gloss papers use the same coating and differ in the substrate and OBAs etc. I think I read a comment to this effect somewhere by printing guru Ernst Dinkla. It would be worth trying the GFS curves and measuring linearity before you shell out for a custom curve.