For those items that are only allowed for approved customers, would the price potentially be different for those customers? It may be possible to combine the alternate pricing you already have in place with the additional list of 'restricted' items. What this would mean is setting up a price list for each customer, in the way that Steve described. I suppose it depends on how you do your alternate pricing that would determine how easy or difficult this would be to set up and maintain. Import alternate price list could be your friend here.
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And Steve, I see you've finally come around to the Canadian way of spelling things and adding additional 'U's like in curiousity...