There shouldnt be a problem using 99% of diesel turbos, just make sure you do the maths to make sure it will work ok. Generally speaking the same turbo will make 2/3rds of the power on a diesel engine as it will on a petrol. So if you get a turbo off a 120bhp diesel then it will be perfectly happy running 180 bhp on a petrol engine. This is only a rough guide though. Also diesel turbos tend to have quite small turbine housings, making them ideal for small engines such as the G40.
Many garrets share component part numbers between petrol and diesel orientated turbos, so I wouldnt worry too much about the quality of the materials, to be fair you probably arent going to be doing mega milage on it anyway im guessing.
Another advantage to running diesel turbos is that they are designed to run a lot of boost, as most TD engines run upwards of a bar. Some older petrol garrets dont like running a lot of boost because of weak thrust bearings, at least with a diesel turbo you know it can handle a bar going to the moon and back.
Personally I would be looking at turbos off 2.0 litre TD engines and upwards. If you find a turbo send me the serial number and I will let you know the specs.