If there are truly are no comps even when they look wider and farther back in time, then the 'party line' answer is that there's no evidence of any demand for this type of product in the market, making it bad collateral for a secured loan. 

If you do one you shouldn't have a problem as now you can use property as cross-collateralization.

@Felicia Dooley Just like regular lenders, you'll want to know their fee schedule, their rates, minimum loan amounts, any cross collateral required, their maximum term, the number of guarantors required, your personal requirements (credit, income, DTI, experience etc.). 

After we owned them awhile we asked to use them as collateral to finance the 20% down to buy another property. 

Is anyone lending money to home owners that are about to lose their home to tax foreclosure and using the property as collateral should they not pay it back?  

Recovered cash plus profit is used in the next deal.Rinse and repeat.      4 - Using non-collateralized loans, where some of the cash from the loan is used as a DP on an investment where the return from that investment (cash flow) pays the debt service on both the investment and the original Loan. 

I have however been told that if I can provide some extra collateral, as well as put one of my parents on the hook as a cosigner, they may work with me.

They gave us a 4.95%, 3 yr term, 20 yr amort, loan with 10% down and some cross collateralization of another property.  

They may want to use your investment property or a car as collateral but it shouldn't be that difficult to come up with the money. 

Depending on your local lenders, this blanket or commonly referred to as a "cross collateral," loan is generally only offered by portfolio lenders or business/commercial banks.