So maybe Luke spent those years learning how to harness the Force to send out strong, focused messages to... and this is where it gets iffy... his old, blue lightsaber which acts like an amplifier, picking up the Force signals from its old master and sending them out to any other Force users nearby operating on his same wave length... which in this case happens to be Rey.
I like it, but I think it depends on who dropped Rey off on Jakku. It also depends on if that was the first time Rey was abandonned (because she was old enough to scream "NO!", remember, and Luke and Leia were dropped off to loving individuals as newborns, not dropped off to some giant gruffy looking alien. I'm guessing here that she was abandonned after the fall of the New Jedi Academy, but that depends on how much older Kylo Ren is than Rey. And too that Kylo Ren never met or heard about Rey). And if it was Luke dropping her off either time, assuming he was a loving father who had spent time with her, he would already have a strong connection with Rey (especially if he's her father!) and he'd call out to Rey the same way he did to Leia on Bespin (except with, as you said, years of focused Force-IM'ing practice
) and wouldn't necessarily need a Force-beacon to relay the message. Besides, I'm kinda partial to the whole "a lightsaber is imbued with the Force" and is semi-sentient idea. The reason the "Skywalker Lightsaber" is kinda messed up and a little dark in it's message sending is that Anakin was good, but kinda messed up when he made it. And then they both (Anakin and the saber) got even more dark after the whole Jedi Temple massacre and trying to kill Obi-Wan. I bet it was glad to be kept in a friendly, quiet box for as long as it had been at Obi-Wan's, it's got some stuff to sort out after all in its semi-sentient mind/spirit. Maz probably sensed that too and back in a box it went. Having the hand that weilded you get cut off not just once, but twice, that's some pretty strong P.T.S.D. for a lightsaber to deal with, ya know?! So, it's calling out to Rey that she needs to get Luke back into the fight and help restore the Light Side of the Force yet again. Perhaps even to help assuage it's own need to be reconciled with the Light Side of the Force.
That's a whole lot to explain in a single movie, let alone a trilogy, and that's just getting started! But it'd be a great Star Wars Lightsaber Novel!
All that and more... Oooooor, it's just that Rey was sent to find Luke, the lightsaber wasn't really trying to get back to Luke, but rather that it liked Rey and wanted her to be it's new owner, and Rey still wants nothing to do with the crazy little messed up lightsaber and is like "Your Luke Skywalker? Good, here's your messed up lightsaber back. It has issues ya know!"
I agree with Bryancd, I think Luke is still trying to figure out his own failure with Kylo Ren and the loss of his New Jedi Academy. But who knows, maybe it's time to balance the Force and Luke is dusting off the scales!
Of course, that doesn't explain why Maz has the saber in her castle.
I think it's likely that Maz, being a proprietor who caters to smugglers, came across the lightsaber via someone who stoll it from Vader (if we're going with EU lore, maybe before the whole Luuke Skywalker plot?) being Force sensitive, she snatched it up one way...or the other.
But I like the general idea in theory — that it took years of concentrated effort for him to reach out across the galaxy using nothing but the Force to reach a like-minded Force user. Too far fetched?
Nope, fun story! Too long, probably for a movie, but not for a novel... get "Dem (finger)Bones" to writing!!!
