Locally, I've managed to acquire some 2.5" - 3.5" HDD connectors.

The box has the following on the front:

DT-327A
3.5" - 2.5" CONNECTOR

it's a small PCB with the requisite connector for the 2.5" drive
on one side and splitting up into a 40" IDE connector plus 5V
power connector and some pins for jumpers.  Local cost was ~$10
each.  I'm still trying to find a mounting plate :/

Darren