It's not unreasonable, if you can find such a sale. To carry a loan, a seller will have to check his mortgage/deed to ensure that they are allowed such a transaction. Typically, most mortgages do not allow this, and so the seller would need you to be able to buy out the current note/balance and then to proceed with carrying it for the balance of the asking price. Ultimately, you would want to find a home with lots of equity, ready to sell, and the seller looking to make long term money vs. short term cash out.
As well, the seller will typically ask for a higher interest rate than what you would normally acquire through bank financing, though of course you would not qualify with a bankruptcy, so you'd have to pay that price to get into a home with this sort of transaction.
Finally, know that these homes are out there, just hard to come by! So, good luck, and let us know if you want assistance in trying to search for one!