This is a warm climate plant. You may achieve seedlings however growing on to a flowering plant in your climate would be difficult.
However, you need fresh seed.
It needs light to germinate. Surface sow and barely cover with seed-raising mix. Push seed down in to make sure there is direct contact with the soil but that they are not buried.
Keep moist but not soggy. Cover container with a plastic bag to help retain moisture loss if necessary.
Will need a min. temp of about 70F to germinate anywhere from 2 weeks to 30 or more days.
Bright light but not sunshine. If you have a propagation box with light that would be good. Germination can be sporadic.
All parts of oleander are toxic, handle the seeds with caution, tweezers best of all but at least wash your hands well after.
After germination they will need stronger light so as not to become spindly.
Because of hybridisation, seed-grown will not necessarily resemble parent plant.