The rental market is pretty hot right now, making rentals difficult to find in the first place.
Many people are facing the same situation as you, having difficulty getting financing to work. Changes to the law (especially Federal law) and changes to regulations implementing the law require higher levels of scrutiny in loan application, greater diligence in verifying borrower information, and tougher performance standards (higher credit scores, paying off past collections, larger down payments, etc).
Do sellers want to sell their homes, yes. Do lenders want to lend money, yes. But there is risk in leasing that the renter simply won't complete the buying process. So, sellers are looking for a very low risk (high degree of confidence) of the sale actually closing. Reducing risk can involve putting substantial renter money at risk for failure - which renters often don't have, or else the seller may wind up with renting a place out that he needs to close and eliminate the mortgage payment on.
Right now I have a listing that the seller is flexible on, but a delay of 5 months would probably ruin the deal. So, on a case-by-case basis some sellers may be willing to accept the risk and the buyer may be able to mitigate the risk (by putting his own money on the line), but nothing is for sure.
You need help finding homes that are ripe for making a deal and you must be willing to do what it takes. Otherwise, plan on waiting until you can get your loan.