The only one I could think of SC is www.brookhousefarm.com at Scamblesby, just off the Louth to Horncastle Road, A153, just South of Cadwell. I've no personal experience, however a friends daughter used to keep her horse on livery there and seemed pleased with the set up.
Sadly, I've not ridden in a long time too SC and even more sadly, I'd now need a stonking great Cob, built like a tank to accommodate me. I've often thought of returning to riding but in my case, I just think it would be unfair on the poor horse