I have two Tourotest 52mm diameter gauges fitted to the binnacle of our 1999 Bavaria. Both bulbs had blown and on removing them from the back of the gauges they are a one-piece item where the bulb is part of the plastic housing with the connection spades. These have been impossible to source. I have however located a suitable replacement. VDO make the same item for their 52mm gauges however they use the mini capless bulbs which are user replaceable. These are a better item that the original fitment. If anyone else runs into the same problem with these, the new holders are VDO part No 05 800 218 and I sourced them through Furneaux Riddall for about £7.50 each.
The attached photo shows the old and new parts.