I'm a fellow Texan (expatriated in Maryland for 12 years) who knows how big-hearted Texans can be, so I've a suggestion that may seem foolish at first sight (but should prove otherwise, in the long term):
You seek corporate donor(s) to provide "Z-rex" for the Smithsonian. Please consider this: If you would announce publicly that you will forego all (above your corporate expenses related thereto) of what would otherwise be your profit in this account, if sponsor(s) will just pay the actual owners' share of your asking price (and if that happens), Jim, that would be "a thousand stars in your crown". Few persons in life ever get or take the chance to set such an example. Surely it would create a goodwill toward you and Fossilnet that money could never buy -- to say nothing of a solid basis for professional respectability by institutions to which, in the future, Fossilnet might turn for investment capital.
Not only that, but it would make you feel mighty, mighty good, "deep down", as my sweet Texan mother used to say, especially if you can do it just because it's the right thing to do.
Furthermore, I think such a magnanimous gesture on your part would virtually assure a corporate gift of the purchase amount to the Smithsonian (helped along by proper media attention). Heck, you mighty even make the front of TIME or NEWSWEEK. :-) Whatever, you'd certainly win the applause of all fellow Texans, millions of Americans, and even of many paleontologists, worldwide.
Do this, and you will personify the epitome of the largess for which the best of Texans are known. I know you've got it in you. Find it. It is a priceless treasure.
Thanks for listening, and, by the way, sniff a few of those Texas bluebonnets for every expatriate when they explode over the Texas hill country this Spring. Your contribution as proposed above would be like the near-intoxicating aroma of Texas bluebonnets: Never to be forgotten. Always loved.