Combination capes can be bought from King Percival in the White knights castle in Falador for 475,781 coins each.
A combination cape can be purchased when the user achieves 99 in 2 skills that are related to each other, the only exceptions being the Monster hunter cape and Skirmisher cape which both require 3 skills to be 99 each.
22400;none;0.7
Arcanist cape
22401;none;0.7
Artisan cape
22402;none;0.7
Botanist cape
22403;none;0.7
Forester cape
22404;none;0.7
Monster hunter cape
22405;none;0.7
Prospector cape
22406;none;0.7
Skirmisher cape
22407;none;0.7
Survivalist cape
22408;none;0.7
Templar cape
22409;none;0.7
Vigilante cape