Transaction Database with Business Sale Price and Contact Info

I'm spending some time over the next few weeks to see if my 3rd party business data sources can help predict business sale prices with any degree of accuracy (considering the number of variables and the sparsity of data, I realize it's a pretty high bar). But I can't build a model without target variables, which in this case is a listing of recently sold businesses with their sale price (so I can target) and basic contact information (so I can append my 3rd party data sources). Any recommendations for the best data source to use for this purpose?

For context, I'm working on a suite of tools to help business buyers and sellers value businesses based on 3rd party data for usage prior to due diligence phase. Clearly 1st party data can't be replaced in the actual details of selling a business, but I suspect there is a lot of value in being able to set reasonable expectations on both sides in advance of committing time and money to doing a full evaluation.