Some mast lights are easy to find but the longer poles with a bend near the plug may not be.
Finding one with to fit your existing base if the light was removable may be harder than finding the whole package, post and base.
If your lamp is a straight mast and is non-removable ( but can be folded down) , there are many options to choose from.
Measure the length of the pole, check if it has a fixed base or not and if it has a bent section.
On some mast lights, there are two lamps, one for running and an all around (both lamps) for anchoring. On shorter hulls, an all around all the time is OK. That is what you probably have but check how many wires are connected. Two wires is a single bulb model but three wires may mean it had a two lamp feature.
Although LED can be quite a difference in price, it is your best option.