These so-called programs are few if not available. I haven't heard one source stating they can actually do this. My answer is simply: You can't find a place that would lend you the money. The simple thing to do is get a gift from a family member and pay them back the gift if you choose to, when you get the tax credit money in the mail.
You can use up to a maximum of $5,000 of the $8,000 tax credit in something that is call "pre-fund" at closing. Ask your loan officer if you qualify for other programs as the Smart Start and others.