The only reason I can think of that a condo complex does not have an HOA is that it is new construction. In that case, the decision-making for the complex shifts from the builder/developer to the owners when the majority of the units have been sold. In this case, you should be able to get a mortgage provided both you and the complex qualify.
You will not be able to get a conventional loan if their is no established HOA. This is because banks want to ensure that rules are regulations are in place to fix issues with homeowners that share common elements. These situations can get messy and it not addressed can drastically impact the value of your condo.