I'm lucky to have three good local butchers who stock high quality meats. However, the meat that is usually on offer seems to have been bred to be low-fat, e.g. a leg of lamb liberates zero juices, chicken only comes skinless, and you can forget about making steak au jus. In the good ol' days, roast beef would provide plenty of juices to add wine and herbs to and then reduce to make gravy, and also dripping for later use. I'm thinking about techniques like wrapping chicken in streaky bacon but there's a limit (really!) to how much bacon you can use in all your dishes. Do you have any suggestions for getting some more fat and flavour into meat?
Surely you can ask for some of the fatty cuts that they might have. Regradless, a leg of lamb, unless the topmost layer of fat has been trimmed (you can tell if it has), can provide a fair amount of juices, although compared to other cuts it's still not very fatty. Good enough for gravy though generally.If you want fatty then ask for necks, beef brisket, spare ribs, breastflap, any offcuts... Even if they don't have them 'out the back', it might be possible that they can source them for you.
By the way- might you also have oven on too high/too long with the lamb?
To more directly answer your question: herbs and spices. Rosemary, mint, sage etc, great with lamb. Coriander seeds, spices etc ground up, rubbed in, marinate if you want. Top with egg yolks, serve somehow with avocado. You could also brine a big cut of meat, but it may not be worth it for you...
You could try lamb shoulder over leg. It's a slow cook, but is meltingly delicious, relatively fatty & divine. Try this: http://www.jamieoliver.com/recipes/lamb-recipes/incredible-roasted-shoulder-of-lamb-with-smashed-veg-and-greens. Ihaven't checked to see if it's strictly paleo or not, but the basic idea is certainly fine.
Personally I try to either go for fattier cuts in general. You could either syringe it in (only works with liquid oil, so most likely EV macadamia nut oil or EV olive oil(make sure you get the real stuff), or use some sort of coconut flour or almond flour batter and fry it. Another option is just making really high fat sauces. If you start with a base of demiglace(AMAZING-worth the time) and add some butter, or coconut oil, along with whatever else suits your tastes, you can up the fat in your meal in no time.