The answer to your question is yes, but if the person selling the home in question is related to you that would need to be disclosed up front. The first thing you would need to do is get pre-approved with a lender who will go over the various financing options available with you, then negotiate a sale price with the owner of that home that is not listed with an agency.
Once you have come to an agreement of price and terms the owner should draw up a contract of sale, my advice would be to seek legal counsel for this part. Once the contract has been reviewed and approved by both parties involved you would them submit that to your lender of choice and follow their guidance from that point. It would make good sense to work with a lender experienced in this type of transaction.