I know this may sound strange but if it's only been one year, there's probably a reason why it still doesn't have a marker. It took us nearly two years to get my grandfather his veterans marker. If you want to mark it with something, I'm sure the family and spirit would appreciate some flowers just to let them know someone else cares for that person.
If you still want to get into contact with the spirit, you could either use a divination tool (like a pendulum) or you could try your hand at something like automatic writing where you channel something directly. Lots of people do it lots of different ways. I'd say the most important factor in choosing the method is what makes you feel safe and comfortable. I'd advise looking around a bit more. If you have any questions about a specific method, I'd be more than happy to answer them.