Have you considered just using a mains switching timer to control the lamp at the line level, just like the timer on many older enlargers?
If you want an always on cooling fan, just get a 12v fan and a cheap “wall wart” type 12v supply to run it separately from the mains.
You’ll find this stuff much more readily than an off the shelf solution to switch 30v at say 3 to 4 Amps for the led bulb.
If you really want to switch the DC, and don’t mind building something yourself, look for a FET switch like this
And build your own timer to trigger it. If you look on line you’ll find lots of simple circuits built around a 555 timer that would do the job. You’ll also need a buck converter to reduce the 30v output lower voltage to run the 555 timer chip, but that could be the same one you use to get 12v for the fan (I assume you meant buck converter not transformer since you are dealing with DC).
Or use something like this