Not sure about abattoirs in your area, although once you have found one you can ask them about grading etc, also check the maximum weight that they will pay for. You should get a grading report back, we have found that you don't get paid for any more than about 21kg deadweight so any heavier is free meat for the abattoir, which you do get paid for if they go to market. Unfortunately one of local abattoirs which would buy from us has closed recently, we used to take in a batch of lambs and could have carcases butchered for our direct customers, who could have the biggest ones, and they would buy the rest so worked really well for us. We are now having to send our spare lambs to market, they always seem to be well treated and calm at the market(fortunately a breed trait to be fairly calm), and I think it helps the markets being fairly small, but appreciate the transport in big lorries in a strange group of sheep/lambs is less than ideal for them and am not sure what distance they are taken.