Moody - there are a few options available. I would say it's better to upgrade than try and find a working Corrado roof.
My experiences to date - I bought a working corrado mechanism from a chap with the initals BR that was sold as working for £200. It broke on the second use. I wouldn't say it was the sellers fault but it's a 25+ year old bit of kit and certainly not worth £200. Don't do what I did - false economy.
I then fitted a mk3 mecahansim with a Passat B4 moonroof. That combo works well - you can get the mech for about £45 (I use Leo GS the mk3 parts breaker on facebook - he is a great bloke and a moderator on a lot of groups). The passat moonroof can be picked up for around £50. I would sell mine if anyone wants it, it needs a new seal though.
I wasn't a fan of the moonroof for my car. I prefered the stock tin panel. I got lucky and Chris F supplied me a bag of sunroof bits for a reasonable sum so I've got 3 corrado mechs built (2 x in car). I can't sell any of these though as I have 2 corrado's and need to keep it for spares. This is the best route to go - buy a broken mech and try and source a bag of bits (the bag of bits only cost me £50).
I've seen somewhere someone has adapted the mk3 mech to work with the corrado inner panel. This is probably the best solution as the corrado mech is weak vs mk3. Mk3 mech out of the box will not auto slide the inner panel. I haven't looked into this with any detail yet.