Do you really want a shiny (slippy) deck
? If not, masonry paints do a great low cost job! If you go that way, am sure you will find lots of advice on the various fora - economic cruisers seem very content with the results. It will also wipe off quite well whilst still wet if it gets where it is not wanted eg cars parked too close!
If you are using a fancy paint and need a lot of non slip powder, I believe monumental masons and the like get quite a lot of marble dust. Otherwise very fine sand (bird fanciers feed it to canaries
I think) sprinkled on top of the paint before it goes off. The surplus is brushed off when the paint is cured!
Some folk use sugar and let it dissolve away to leave a rough surface but I haven't tried that! Best talk to someone who has used the paint you decide to go for if you are not sure.