Any owner who has enough equity to consider carrying back financing for you is going to want a min. of 20% down, there's a reason why you can't get traditional financing & because of that risk any owner with enough equity to consider this for you needs to feel secure with this decision. That also means that an owner carry seller will likely charge about 8% interest.
I know of 1 owner carry seller in my neighborhood (not Riverside) & they're asking for 10% interest. That's a little high. You should really speak to a mortgage lender, you may actually be able to qualify for an FHA loan which takes buyers with a credit score as low as 580. Your 5% down can go towards your 3.5% required down payment, plus all or part of your closing costs should you not be able to find a seller or bank willing to pay your closing costs for you.
If you find you might need to rent first while you fix your credit, please do NOT get into a lease option agreement, just rent & if anything, add a clause to your lease agreement that simply states "I reserve first right of refusal should the landlord choose to sell during my lease term".
Commute from Corona to Anaheim, take the 91 freeway & get a FasTrak Pass, go to google & type in "91 express lanes california".