hehhe, this is very old, but I will answer in case another person needs.
To get a NSView to place a control, you need to place in your form some kind of empty windowed control (which means a TWinControl descendent, which has a handle property). The best would be writing your own TCustomControl in code, and search the wiki for instructions for that. But if you are more lazy, just use a TPanel or TPaintBox or maybe TImage.
Then to obtain the NSView from a particular control:
1> Make sure you are using the LCL-Cocoa widgetset
2> use this function from unit CocoaUtils:
function GetNSObjectView(obj: NSObject): NSView;
Like this:
uses CocoaAll, CocoaUtils;
var
MyControl: TCustomControl;
MyControlNSView: NSView;
begin
MyControlNSView := CocoaUtils.GetNSObjectView(NSObject(MyControl.Handle));
and ready to use the NSView! =D