I have to be brutally honest here, knowing what I know, I would suggest your son begin considering a career other than baseball.
You talk about his career running out, but I don't see it as a career as he isn't playing or being paid to. I am not understanding how close you feel that he has gotten, because someone signed him up to play independent ball? I am going to assume your son is about 23,24 way too old for the first level of pro ball where the 17,18 year olds begin (and those on rehab). That alone is the greatest odd against him.
IMO training centers can be just another group of blood suckers for those that are willing to dump in their hard earned dollars. The serve a purpose, but in your case sounds like they never came through for you.
Last year my son's BF a second round pick (pitcher) was released from the Mets, he went to play Indyball this season and left because he realized he wasn't going to get picked up from there and it wasn't worth the risk of getting hurt. He will begin training again this off season, has moved to FL and will with help of his agent get tryouts for next spring, he might get a chance because he is a pitcher, but other than that he realizes the odds are NOT in his favor at 26.
Your son being a catcher makes it even more difficult. You should actually do some homework on milb catchers and see why most don't stay at that position unless they hit the c rap out of the ball.
Baseball training is not playing the game to get better something your son has not done and something that needs to be done for someone at that position.
CD is correct about how hard it is to get an agents attention. Their sole purpose is to make money from you from you signing your first big league contract but advice is free and I will bet they will tell you the same you have heard here.
I may not be as kind with my answer, but I see how hard it is for the ones who have been playing for years and won't ever get to reach their goal (ML). I think the biggest misconception is understanding how hard it really is, and if your son had a tough time on the lower indy level (whatever that is) you cannot even begin to imagine what it is at the pro, even at the lowest pro level.
I admire the determination as well, but sometimes one just has to be realistic and it is hard to be if you don't really know how difficult the uphill battle is, even for those with more experience and talent. As far as people telling you stuff, everyone tells everyone stuff to make them feel better, the best people who are up front and honest and tell you the truth are the ones they often end up listening to(sometimes what you don't want to hear).
Your son's career in baseball does not have to end, there are so many ways to stay close to the game, I would suggest that they perhaps become a strong consideration at this point.
Best of luck.