I have seached the internet to find danish stores that sell acid dyes. Found 3: Lanasyn, Remazol and Irgalan. They all have to be mixed with vinegar + other "stuff".
I have borrowed a pile of books about dying. One of them is particularly good: Yarn to dye for by Kathleen Taylor. She uses Gaywool dyes which can be ordered here. Again you have to add vinegar and urea.
I have been to several indian/asian shops to bye food colouring powder -never managed to find blue.
I have been to several hobby stores, paint stores etc looking for acid dyes -they all looked pretty puzzled when I asked about it! The only thing I got was a headache (and a pair of sandals but that a different story).
But why in the world didn't I just do the most obvious thing. My Secret Pal has explained how she dyes, she has send me yarn with colours I like. DOH!
I have now ordered the same dye as she uses. Omega dyes -all in one acid dyes. 7 different colours. Postage was only 4 GBP the colours just 20 GBP. That is SO much cheeper than the dyes I could get from danish dealers.
Marine Blue (25g)
Mail Red (25g)
Naval Blue (25g)