if it's not confined to a specific category or two, there might be something to try that we have not officially explored:
you can alter a page layout (productPage.inc and/or any category specific versions) and check for select products by ID and then display a "call us" type message and forego the add-to-cart buttons. the list of products can be a file that is read in, if not it might have to be list present in the code (agorascript).
Like I said, nothing like this has been tried officially, but it is something to chomp on fer a person with some basic coding skill.
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