Is there an anti-slip paint I can use on my internal stairs?

Never done this but couldn't you add sand to the paint?

There are several on the market. Some made specifically for the type of material you are painting. My Dad used it on the ramp into the house for my Mom, would wonderfully.

Some products to give you an idea of whats available ♥

https://www.amazon.com/non-skid-paint/s?ie=UTF8&page=1&rh=i%3Aaps%2Ck%3Anon%20skid%20paint

there is a sand type additive for paint to make it less slippery, and there are gripper strips that can be placed on the treads as well.

anti slip garage floor works on other floors as well

On a boat, sand is added to the paint to reduce slipping. It is available in a variety of options. It is also added to paint used on a garage floor to increase traction. Talk to your favorite paint store. They all have it. There are also stick-on pads, but they are more suited to industrial applications.

I know many people add sand to the paint but it periodically needs to be repainted because the sand wears off. If it is not a staircase in the living wall or main hall where it is seen all the time, maybe you could consider putting down the anti-slip strips they put on the bottom of bathtubs. Try asking at a floor dealer, they might have great ideas.

You should be able to add sand that is made for non skid. Add the sand a little at a time and make sure you keep mixing it, because the sand settles to the bottom.