I think Tek Tanks do some senders, but not sure whether they are VDO, but they may be compatible. See www.tektanks.com or perhaps it's .co.uk - not sure...
Do a search on ASAP Supplies. They have the VDO sensors that you require.
I struggled with one of these for a couple of years and eventually replaced it with a clear plastic sight glass into which I placed a weighted fishing float (red). A quick glance tells me how much water I have.
