There are always some lenders (often quite large and well-known institutions) that will hold a certain portion of their mortgages as "portfolio loans."
Quite simply, a portfolio loan is held by the original lender for the duration of the mortgage. For this reason, these loans don't have to meet federal requirements for mortgages that are re-sold on the secondary market.
With a portfolio loan, you can avoid some of the most common issues that borrowers face when getting a mortgage on a condo/townhome, such as not enough owner-occupied units in the complex to meet federal guidelines. Good luck with your purchase.