Well, unfortunately, I had no luck with gardentractorspares in the UK.
Their reply was: -
"I am sorry, but I am unable to help you with this gearbox. I have spoken to my Peerless expert Graham and he has said that the part you require is a precise piece of the gearbox and you will not find a secondhand part for this and also I have no reconditioned gearbox available.
I also e mailed Peerless you enquiry and this is their reply below:
This is an elderly model VST 205 transaxle.
Unfortunately there are no replacement units for the Peerless hydrostatic VST 205 and VST 705 Series available anymore.
All sold out and the factory does not supply replacement units anymore since the year 2005. The last batch of OEM production units were produced back in the year 2000"

Let's hope Nowra Mower Wreckers has some better news.
Still want to know about doing a changeover from this model Peerless or to another manufacturer.
Thank you
Daryl

Environmentally friendly recycling at it's best