Jane, re the Similasan eye drops, you may be able to find a bottle or two at a local store. Since it wasn’t recalled there will be bottles on the shelves until they sell out. I’ve had good luck with this approach when a product I learned that a product I like has been discontinued.
As for alternatives, have you tried Optique? It’s a homeopathic product and, like Similasan, contains euphrasia (also known as eyebright). I’ve used it, but only for dryness, never irritation. Natural Ophthalmics has Ortho-K for irritated eyes. I haven’ tried it, but I’ve been very impressed with other products from them that I’ve tried. Blink claims to address irritation, but I haven’t tried it. My optometrist likes it. I do like Thera Tears singles, which I find soothing. My eyes are mostly dry, rather than irritated.