I'm currently making two shafts for two spears, and to do so in January I've cut down two relatively thin hazelnut trees, and kept at about 3 metres length; I don't really need them properly seasoned, but they have several bends which need addressing. To try and straighten them I've tied them tightly against a cement pole the day I cut them down, and I've left them there until today (Monday). I need them mostly straight in about 3 weeks, is there something I can do?
I saw on the woodwrights shop them steam bending a long piece by putting it in some metal ducting and piping a regular tea kettle's steam output into it. The far end got stuffed with a towel loosely. After about 20 minutes they were able to bend an oak bar into a U shape by hand so if you have some straight reference and enough clamps I would think you could straighten a spear shaft in the same way.