"What else can you use besides saltpeter to make combustible cartridges? I cant find any where I'm from."
Collodion, which is cellulose nitrate dissolved in alchol and ether.
In the 1800s Colt and possibly other companies provided unitized cartridges where the powder charge was adhered to the bullet with collodion.
Collodion was apparently used to coat a mold and the powder was poured into the mold and a bullet seated. When the collodion dried, you had a complete cartridge (sans cap, of course).
The collodion was tough enough that the cartridge would stand up to fairly rough handling, and more importantly, it was waterproof.
Upon ramming the bullet home, the force fractured the collodion "skin," which allowed the flash to ignite the powder.
Collodion cartridges survived right up to the advent of metallic cartridges.
More information, and a picture, at this site:
http://www.christchurchgunclub.org/html/cgc_art_pc1.htm