Good question: IIUC, a -25 is an Agusta unit. The Bell equivalent is a -025 (at least, that's how it works for tailbooms!).
You could try looking at the HELPS section on
www.rotor.com - it's like Partsbase for poor people, though often a little out of date! Under -25, there are 3 showing (all in Oz)...add the '0' and there are 13 there!
WLM, I bought a -029 tranny from Canada, 0 TSI and 250 TSO, cost me $29k in 2004. That was from Tempest Heliparts....contact there is Laurie Saindon.
Also try Sean Sinclair at Aeroproducts in Scottsdale too - he's a great guy, he's helped me a lot over the years. Tell him Rob from the UK sent you!