SWERHP,
First of all I wouldn't bring him here until his velocity gets into the mid 80s range. My suggestion at this time is to contact some good academic DIII colleges. There are many of them where he can play. You just have to find the right one.
Much of DIII recruiting is done by player contacting the school and showing interest. There is this misconception that all the DIIIs recruit heavily. Of course, there are a few DIII that do recruit hard, but the majority take what they can get. If you contact a dozen DIII schools expressing interest, you will see for yourself that they will also express interest in you. I've often wondered why players spend money to attend showcases to get a non scholarship college interested.
There really isn't much reason to attend a showcase, especially one that will cost you a lot in order to find a DIII school to play baseball at. Most important is that the player qualifies for admittance.
You will need to do a little home work targeting the colleges that best fit your son. I wouldn't target the top level DIII colleges because making the roster would be a gamble. Some have very good baseball programs. However, there are hundreds that will welcome your son with open arms if you show interest in them. And many pitchers really develop a lot once they are in college.
If your son continues to develop over the next year you can then change your plans. But I would start by contacting some DIII colleges. I think it will give you a secure feeling that your son will get an opportunity no matter what happens. Once again, please understand that there is a wide range of DIII colleges and baseball programs. They range from excellent programs that can compete at a very high level, to those where any warm body is on the roster. Your son's accomplishments and ability will not get ignored if you contact the right colleges. Best of all, it won't cost you anything to find out.
I'm only basing this on what you posted. Pitchers often improve velocity a lot over a year or two. But currently throwing 76-78 is probably not going to draw enough interest in scholarship schools to justify the amount of money it would take to attend a showcase event here in the USA.
Best of luck and let us know how things work out.