Mains AC -> 12V DC, 100W - that's a very common power supply specification, and particularly for photographic enlargers, so I wouldn't have thought there would be too much problem finding something suitable.

If you can't find a used one, it should also be easy to find a new alternative, though obviously you might have to cobble together the appropriate connector to actually plug it into your enlarger. A quick google turned this up - AC DC Mains 230 12v Output Max 20 A DC transformer, but I would have thought it ought to be possible to find something cheaper.