ITC is the manufacturer, they make the fixture both in a screw in and a spring mount application.
3 Inch Size:
https://itcshopnow.com/products/radi...39602522030116
4.5 Inch Size:
https://itcshopnow.com/products/radi...pr_seq=uniform
I’ve had to replace all the 4.5 ones on my coach, and have bought both on Amazon and direct from ITC over the years.
Of note, ITC also makes a version with a plastic lens, the above is glass which is what my coach has, but depending on your coach the plastic option is there as well and is slightly cheaper,