I think the bottom line with this, is that the chance of seeing a commercial system for the hobbyist is slim.
In a nutshell, if you desire such a system, it's most likely going to be a case of rolling up ones sleeves and building it. Model submarines is a very niche sector of the hobby, most of those in the hobby are satisfied with the performance of off-the-shelf kit, as it works adequately for most purposes even though the radio isn't giving its best performance in such an environment.
There is a concern in some quarters that 40mhz radios are going to become unobtanium in the future. Whilst I agree that the big Japanese and European companies will (are?) phase out there 40mhz range, it appears that smaller Chinese companies are stepping up to the plate to fill that sector of the market.
Whether these sets are as well made as offerings from other countries remains to be seen, although many folk are using Chinese built 2.4ghz systems and ssem to be happy with them. There is also an awful lot of S/H sets out there kicking around.