Testors Dullcote has, I believe, had its "new" EU formula for at least five years, probably more, and since then supplies have sometimes been intermittent and there have been rumours of Testors' demise. However, it now appears that there may be some truth in these rumours, at least as far as sales outwith the USA and Canada are concerned. According to an American forum I've been reading, Testors are owned by another company, Rust Oleum, which itself is owned by yet another company, and apparently back in October last year Vincent Pierri of Rust Oleum said: ""Rust Oleum is no longer selling the Testors brand internationally, through distributors, but continues sales and distribution in the United States and Canada without interruption."
Whether that has actually happened is unclear. Latest US rumours are that Testors has closed completely, but these have been denied by Rust Oleum who say that Testors is their leading brand and is being fully supported. However, if you like Testors, it may well be worth stocking up. For myself, I like Dullcote but not the way it sprays, which is too heavy for my liking. I've read some excellent reports about Winsor & Newton Galeria Matt varnish, with some users saying that it produces the mattest finish ever, and so have ordered a bottle to try it, one advantage being that I can airbrush it on as lightly as i want.