9 year old boy socks and and boxer issues

Please help !

My 9 year old boy does not like socks that slip down. He is currently wearing long grey little grippers which go up to his knee under his trousers. The company have stopped making normal ankle high socks and I really need to get hold of some for when he starts wearing shorts. 

Also, his boxer shorts have a hidden pocket where he likes to tuck himself in. We got them from Tesco but they don't seem to make any more like this. Does anyone know any where that sells boxers like this ?