Keiko, I'm glad to hear that you're in a great position so far as Spiritualist churches are concerned! And you have the right attitude. DON'T go with the idea that you'll receive a message that day. You may. You may not.
I never was interested in any of this until my wife died in July 2010. One thing lead to another. First I started looking into the near-death phenomenon: then into Spiritualism. I've never been able to get a real, personal reading, but a UK friend did a couple of them for me, remotely, as much for the experience of trying to do them from a distance as anything else.
Most of what he received was, to me, gibberish, or messages intended for someone else. But he did supply me with some good, solid evidence, about/from my wife and some other people - information that he could not possibly have gotten from the internet or from me - that was QUITE evidential. I don't say, "conclusive proof ", but "quite evidential".
Also: for me at least, Spiritualism has ceased to be primarily about receiving messages from/about my wife, and more about the afterlife, as such. Maybe it will work that way for you, too.
Also, even if you don't receive a message from your father, a study of Spiritualism will reveal the many messages so very many people have received in the past. Many of these people started off as skeptics but became ardent believers. Is there any reason to suspect that your father, my relatives, are not enjoying a happy afterlife as well?
Otherwise: people ask me sometimes if "it gets better over time". My answer, as time has gone by, is that IT doesn't get better - your loved one(s) are still gone - but YOU get better, in that you get stronger and better able to handle the loss.
It also helps to do something in your loved one's memory. I started a book trust at my wife's college, had a bike rack installed in her memory outside our church, and am having a small monument erected on her college's grounds (she was a Professor of English).
Jim