Regulate high negative voltage (below -30V)
They do exist, you just need to use an inverting controller with external switch, e.g. LT3757. Then you can up the voltage rating of the external switch to whatever output voltage you would like, plus some margin of course. Practical tip: make sure you read the datasheets well. If you're inverting a fairly small positive voltage into a large negative voltage, you will need very high duty cycles. Not all dc/dc controllers will support this.