As other answers have stated natural lodestones may be too weak to create the magnetism you require for "enchanting" your weapons.
We could consider however how lodestones themselves are created. From what I have (briefly) read on the subject they can be created by lightning strikes. If a lightning strike can magnetise an object, perhaps your primitive civilisation could base a religion around "The Thunder Gods".
They could construct obelisks or tall monuments to their version of Thor that are essentially just massive lightning rods. These places of worship would have the 'magical' abilities to bless iron weapons placed upon an altar at the base with the power to slay these demons plaguing your people.
When lightning strikes to monument it is carried down to the altar and into the object placed there, magnetising it in the same way lodestones are created. Now this may require some handwavium-supercharging of the numbers involved to create the field strengths you desire, but I think it would add some amazing depth to your civilisation as they would base a lot of culture and reverence around the thunder god's protection of their people. Storms would become times of great celebration and your warriors in training could complete a rite of passage during them, placing their personal armaments in the altar and holding vigil awaiting the "Blessing from the sky". To be "Thunder-Touched" would be a massive morale boost. Whilst rare for regular villages to have lightning storms, certain areas in the world do have higher frequencies of lightning strikes and your people could congregate in those areas, constructing multiple monuments and eventually becoming a religious hub akin to mecca that could be a destination for pilgrimages for those completing their warrior training. Also this would provide a natural deterrent to the enemies as the area would potentially be highly magnetised itself.