Unfortunately I don't see it in stock anywhere, which makes me think that it might not be manufactured any more. Sorry to be the bearer of bad news. Most of the places are also in the UK. I thought that might mean it was a UK-based company, but it's in the US.
Out of stock, but if you wanted to, you could try contacting one of them and see if they know anything about it?:
https://www.emeraldcrafts.co.uk/stit...ible-thread.ir
https://www.createandcraft.com/gb/pp...d-clear-189845
https://jet.com/product/Invisible-Th...d06a605df87648
Ridiculously expensive:
https://www.amazon.co.uk/gp/offer-li...&condition=all