Most slow bred/traditional breeds are more fatty than is currently sold in supermarkets. Having said that the producer influences the final outcome too. In particular smallholders producing just a few pigs per year often 'overcare' for their animals and start off with very fatty animals indeed. This usually revolves after a few seasons, particularly if you give your producer feedback - so the first thing to do is to talk things over with him/her.
The second thing is to either trim off some of the fat and render it down/do something else with it (toucinho, lardo etc), or to reduce the overall fat content by mixing it with a leaner cut.
For a local producer of slow grown quality pork I'd have a chat with your local abattoir and ask them for recommendations.
Depending on where you live you could do a lot worse than checking out these folks (and it wouldn't surprise me if Debbie is a member of this forum):
http://www.hiddenvalleypigs.co.uk/pork.html