If you don't find one anywhere else, there's a shop in York in England that might have them, I know they had a few gunderson sets in stock when I went in there middle of last year.
With the exchange rate being so low, it might not be too expensive to get them to you either.
Hopefully I'm not breaking any rules by providing this - they have an eBay shop which has nowhere near their full stock on there. Half their bricks and mortar shop seems to be full of Atlas O scale, whereas their eBay shop only lists two items. I guess it's too much of a hassle for him to list them all?
Maybe message them on eBay to see if they can help?