Unless there is an incredibly strong reason to use Ada for this application (e.g., customer demands it, or you already have a big application coded in Ada that you want to use), it will likely be a lot less painful if you just bite the bullet and code your solution in well-crafted C99 or C++ as you see fit.
If you insist, Sofcheck's translator might be best; they've been working on it a long time.
Failing that, you might(?) build a translator starting with the ASIS output of an Ada compiler. That's likely rather a lot of persnickety work since Ada has pretty precise semantics that you'd better preserve if you want to just carelessly code in Ada, translate and run. It will be even more work if you want the output to be "pretty" for the final customer. (Long term maintenance should be a consideration). I suspect implementing code to simulate Ada's rendezvous might be rather tricky, being both semantically complicated and asynchronous at the same time. The real flaw with this approach is that it is a lot of work; maybe just getting on with your life and coding the application itself in something non-Ada would be less effort.
See my caveats on language translation done poorly and alternative methods.
