I'm not sure what type and size boat/ship you need running lights for, but I usually scratchbuild my own. You can barely see the starboard running light on the mainmast shrouds of this Ketch, in HO, but it is one that I built with strip, and rod styrene.
With the styrene you can come up with something that is reasonably close to the proportions of an actual running light.
In this shot of my coastal freighter ( modified Lindberg Trawler )
You can just make out the port running light, on the pilot house roof, (also scratch), and the Masthead light, and stern light, which were casting from the kit, "cleaned up".
In this shot of the "towboat", the same things were done.
Pilot house close up.
Yeah, the "Towboat" is a modified Revell Harbor Tug kit. The pilot house, stack, and engine room skylight ( hiden by small boats ) are all scratch built in styrene.
We always learn far more from our own mistakes, than we will ever learn from another's advice.
The greatest place to live life, is on the sharp leading edge of a learning curve.
Lead me not into temptation.....I can find it myself!