How long should I cook boned shoulder of Lamb?
Shoulder is a tough cut. I think you will probably find it a bit chewy if you've cooked it at 190ºC for 52 minutes. In future, preheat the oven to maximum, place the lamb in a roasting tin, cover the tin with foil, put the tin in the oven, then immediately turn the oven down to 150ºC, and leave it for 4 hours. After that time, take it out of the oven and let it rest for 30 minutes or so. The lamb will melt in your mouth.

And yes, you can buy a bone-in shoulder at just about any supermarket, and they are usually tastier. Cook it as above and you will just be able to pull the bone out of the meat.