As you say, you can buy the Volvo Penta
DS components, but they are also available from Teleflex, Morse, Uflex and others.
Another way to do it, although somewhat more expensive, is to install electronic controls. That way you can "drive by wire" from any number of control stations anywhere on the vessel without worrying about mechanical cable routing issues.
Some of these suppliers are Twin Disc, ZF, Uflex, Glendenning and many more.