It is Holson Products (close!) I don't have the # on hand, but you could probably find it by searching this board.
I would not recommend adding extra pages to the WDW album though. The rings don't seem to be able to take it and they come apart...letting your precious pages loose (or, should I say "my precious pages" as this is what has happened to my WDW album!) I think if you're going to add more I keep it to 20 or so pages total.
I don't mean to be discouraging, but I don't want anyone else to have to redo theirs like I have to!