The old-school way to do it for a single object is with GetValue.
To get a collection of objects, use the XSICollection.Items property.

# Python
from sipyutils import disp        # win32com.client.Dispatch

allColl = disp("XSI.Collection");
allColl.items = Obj.FullName + ".polymsh.cls.*.Material"

// JScript
var allColl = new ActiveXObject("XSI.Collection");
allColl.items = Obj.FullName + ".polymsh.cls.*.Material"