Not aware of any special programs. . . .you wait until you sell current home to buy new home. . . .
CAN you convert your home to rental property and cover your PITI (principal, interest, taxes, insurance) plus other expenses(maintenance, repairs, improvements) on home?
Not knowing your finances, can't say whether you would qualify with carrying this debtload as well as wanting to assume new debt for new home. And if your finances are down, it's unlikely.
0% down loans are a TERRIBLE idea. You end up paying SO MUCH interest over the life of the loan, you will have paid for your house several times over, due to compounding of interest. Even IF they would give you the loan, is it worth it to buy a home and pay for it 5-10 times purchase price?? You may qualify to apply for a USDA loan, but that doesn't mean you will get loan approval. They have run out of money very quickly in some parts of the country, and loan approval is based on the whole package of you two: credit rating, stable employment, adequate income, sufficient down payment, low debt load. The MORE you put down, the more likely you are to obtain loan approval, and the LESS you will spend in interest (tens of thousands of dollars) over the life of the loan.
Suggest you figure out how to make current home work for you, and be more realistic. Re-arrange things, finish a basement or attic or do a small addition.
Just because you want something, doesn't mean you should have it, or can have it.