Proof of funds...listing agreement

I am working on a short sale and the mortgage company is requiring proof of funds and proof that the house has been listed before they will look at my package. This is a stigmatized house that is in very poor shape. I don’t have the funds to buy it and intend to have a double closing. So where do I find an “old” listing agreement and a proof of funds letter? Do I actually have to apply for a loan with someone? Thanks!!! Everyone on here is so great to help up newbies!!!