The new connector is more secure and less prone to breakage than the older connector, especially if you lay down the transmitter or it fall onto its back. The trainer cord you need is:

FUTM4420 MDTC TRNR CORD MICRO/ROUND PLG $19.99

These parts can be ordered through any hobby retailer who sells Futaba systems and accessories. They are currently out of stock, but due to arrive in the next couple of weeks or so. Get your order in to make sure you get one.

The RealFlite controller cannot be used as a trainer box with a Futaba transmitter. They are not designed or intended for such use.