Soluble glutinous rice starch can be hard to come by, but can be made at home:
"Glutinous rice is polished and soaked in cold water for a week. This is then steamed in a steam basket and pounded into a cohesive mass. The mass is stretched into a thin plate like a squashed cake, which is parched at a suitable temperature. The parched cake is ground into a fine powder. The powder is somewhat brownish, but has a large cohesion power and is perfectly gelatinized in combination with water. This is the most useful binding agent for firework stars." - Shimizu

I have recently made some SRGS: soak rice in cold water for a week, steam for an hour, dry out in oven. Powder in coffee grinder. All worked fine but seemed a lot of effort and time consuming. Second attempt: put dry rice in coffee grinder mixed resulting flour with water, brought to boil and simmered for 15 minutes, stiring continously. Transfered resulting 'glue' to low oven to brown. Put dry mixture in coffee grinder to produce identical SRGS in just over two hours.