This list may help..
http://www.mangago.me/home/mangalist/224/
http://www.mangago.me/read-manga/tsuki_to_yabanjin/
http://www.mangago.me/read-manga/taiyou_no_kikoushi/
http://www.mangago.me/read-manga/koi_wa_maiorita/
http://www.mangago.me/read-manga/ousama_game_takagi_ryo/
http://www.mangago.me/read-manga/the_hinanomori/
http://www.mangago.me/read-manga/oki_ni_mesu_mama/
http://www.mangago.me/read-manga/kiss_me_princess/
http://www.mangago.me/read-manga/hashire_oujisama/
http://www.mangago.me/read-manga/kouya_no_seifukuou/
http://www.mangago.me/read-manga/flower_of_destiny/
http://www.mangago.me/read-manga/black_knight/
Lookong for yaoi/shounen ai with kingdom/royal theme :D
Thankyouu