Have a look at the Griffiths Mill website, and also the Halifax fella. (Will dig his card out and put proper name of company.). Both will do any quantity from one fleece upwards. Natural Fibre Company are very good, but minimum 20kgs - so you need to save up a few years' clips if you've only a few sheep. Or go into their mix-n-match scheme, where they combine similar clips from several flocks.
In all cases, you need to skirt thoroughly yourself, only send good quality fibre. They'll process all you send. Washing/scouring removes some weight - typically 25%, can be more.
Some charge on weight submitted, some on weight produced. Each process is charged for - scouring, picking, carding, combing, spinning, plying, balling. The NFC website has a good explanation of all the processes.