Textured materials containing large particles such as sand, would block an airless spray tip, so you pump them through a large tip or nozzle say 4 - 8 mm diameter into a chamber in the gun where you introduce compressed air to blast it into a spray. The pump needs to be able to handle the textured materials, which means large valves and a long stroke if it is a piston pump.
Graco President 10:1
pneumatic piston pump
HAMA MC3V worm pump
If the material is solvent based, you should ensure that it is compatible with the pump, for example the President 10:1 is compatible with most solvents, but a worm based pump is usually not, because the solvent will probably attack the rubber stator.
Hopper gun
If you only have a small amount of textured material to spray, you can use a hopper gun, which costs less than £100, but it is heavy when filled with material, so is hard to use for more than an hour or so. All you need is a good supply of compressed air, say 15 cfm.