I think that most mills require a minimum weight of fleece of 20 or 25 kgs to do a spin run - their machinery is large and less than that is just not worthwhile. However, you could try Halifax mill at Goole where I think they have the ability to spin small amounts as well as whole batches. They are a very helpful lot.
You could also try the various Mini Mills around the country, where they will do smaller amounts, but I seem to remember they are proportionally more expensive than a larger mill and have a long waiting list.
I have a Herdwick sweater which my MIL knitted for me many years ago - it's still pristine as it was so painful to wear, and very hot, that it's had very little use.
I really really would advise you not to knit a scarf
The skin of the neck is very delicate and you wouldn't wear it more than once. Boot socks now would be perfect, or gloves