Further to my last post I found my copy of Marius Besson, ”Un recueil de sentences attribué à Isaac le Syrien”, Oriens Christianus 1 (1901): 46-60, 288-298. It has also been reprinted by Gorgias and may be obtained (at a price) from http://www.gorgiaspress.com/bookshop/p-57035-besson-marius-un-recueil-de-sentences-attribu-isaac-le-syrien.aspx.
I recollect now that the reason I did not include Isaac’s work in my book on the two ways is less that he was remote from the tradition, though he is, but more because the relevant material appears only in a few sentences towards the beginning, whereas there is a great deal of other material. Nonetheless, I realize now that this is another ascetic gnomologion. Given my interest in these, sparked by working on the Gnomai of Nicaea, I do now regret failing to give this work any further attention. It provides yet another instance of the asceticization of the Church Order tradition and the growth of the classical tradition of gnomologia as means of instruction and self-instruction in monastic circles.