It isn't just about piling in calories either, you have to find the right dietary balance for lean mass growth, especially being a hard gainer. Don't hold back on any body part while waiting for a stubborn one to catch up. If you added 3 inches to your calves and stayed the same everywhere else, you would look unproportioned. It takes time to grow noticeably, try upping your calories a few hundred for a couple weeks, if you are not gaining fat, up them a couple hundred more for a couple weeks. Give yourself a few months and remeasure to see if anything changes. Just for reference, I put on 15lbs in my first 7 weeks on cycle and have only put a half inch on my arms, but they look like I put on much more.

Maybe back off the cardio training and hit the weights some more, try a new split, shake things up, shock your body into a growth spurt.