The Federal Veterans Administration provides a loan guarantee. These loans are offered by banks and loan borkers. The maximum zero down VA loan is about $417,000 these days.
As your purchase price is $640,000, A lender is likely to require a substantial down payment even with the VA loan guarantee. The US VA does not put a maximum on the amount a lender will lend They are only limiting the amount of the loan that the US government will guarantee. So it is possible that you will be able to get close to the 95% financing that you require to complete your purchase. There are several loan brokers here on Trulia Voices ( you can check their profiles) that may be able to give you more specific advice if you email one or more of them.
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