There are also various people and companies who will buy Shetland wool - if it is clean and well skirted. Ask the Shetland Sheep Society, Mull weavers, British Coloured Sheep Breeders Association (who will give advice on the quality and preparation of fleece to be offered for sale) and some of the spinning supplies shops who may be looking for fleece to sell on. Fleeces offered at Wool Fest must be very clean and well presented. You could also look to getting your fleeces processed into roving or tops at somewhere like the Natural Fibre Company, then selling it on to spinners online. Fleeces can also be sold in their raw state online but again be sure you have picked out the best.
I have strong feelings about giving away fleece, to do with the psychology of it. If someone gets something for free, then they will not value it. What you are saying in effect is "here is something I would otherwise throw away/burn, but I'm giving it to you". If a spinner is going to spend months working with a raw fleece, she will want to choose the best she can buy - clean, no veg matter contamination, no crayon marks, sound staple, evenly coloured, the appropriate crimp for her project, unfelted, the right colour esp in Shetland fleece, and so on. In other words not every fleece offered is going to be suitable for spinning - you can't make a silk purse out of a sows ear !!
Few modern spinners have room to store more than a couple of fleeces, so they will be very picky about what they can give house room to. Also as Anke says, many spinners buy ready dyed or carded fleece, to save having to deal with a raw fleece. Spinners today are absolutely spoiled for choice with the amazing variety of fibres on offer - not just wool, but alpaca, quiviut, angora, camel, cashmere, ramie, silk, on and on, in any stunning colour you could ever want. So to sell your fleeces to handspinners, you need to tempt and woo them, not offer to unload a whole trailer full of raw fleece at their doorstep. In fact Edinburgh spinners have opportunities to buy some of the best fleece to be found in Britain when they go to the Broughton gather, and they are remarkably picky about even that !! Try contacting the BCSBA (above) for more info on how to market fleece - they have been doing it for years.
I think maybe you have missed realising that far from being wannabes, many spinners are highly skilled crafts people and know exactly what they want. Or if you are a skilled salesperson, you can convince them that what you have is what they want - at a price !!