**ahem** The same unnamed mutual friend sent me on a Flump quest in January. If only you had talked to me, Darren.
I did my internet research before arriving in London, never having heard of a flump - and once having heard of it, bemused that the friend who can love Hermes can also eat flumps.
I found flumps - the kind that are about the length of a candybar and sell for just 11p - at Sainsburys. I bought a handful, but I knew this is not what our flump devotee prefers. I had no success on other central London flump stops. However, flumps were found at Heathrow in the configuration she enjoys.
Of course, this mutual friend needs to acquire a mailing address in order to receive any of flumps. So here they sit in southern California. Somehow, I don't think twisted marshmallow things have a shelf life, so the only downside of her delay in receiving them is her continued hunger for them - thus your search.