Coving ~ Small plain 30mm x 30mm polystyrene

Hi All, Help. I've recently done some DIY which involved removing 2 No. short sections of the original polystyrene coving (55mm long and 75mm long). Foolishly I threw out the peices as they were damaged anyway, however I've been all over the local DIY stores and the internet and cannot find anywhere that does a simple curved cove that is 30mm along the wall and 30mm along the ceiling. As the flat was built in the early eighties, I assume this also dates back to that period. Does anyone know where I can find a plain curved 30mm by 30mm coving? As the room is quite small I don't want to have to replace the entire thing with bigger which is my only other option to put it right.
Thanks in advance
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