I recommend just searching for sold listings on ebay. I have seen several unopened listings at least in Europe lately.
Although I don't think that the number of unopened SMS2 is that small. I remember when our local Toys R' Us did their clearance some time in the 90s and over one hundred unopened SMS2 were on sale. I assume that it was similar in other locations. Unless those units all went to the junkyard, there should be quite a number still around dampening prices.