First init your atlas like this:
SKTextureAtlas* myAtlas = [SKTextureAtlas atlasNamed:@"MYATLAS.atlas"];
Then you can load all textures into an dictionary
NSMutableDictionary* texturesDictionary = [NSMutableDictionary dictionary];
for(NSString* textureName in myAtlas.textureNames){
SKTexture* texture = [myAtlas textureNamed:textureName];
[texturesDictionary setObject:texture key:textureName];
}
or just preload atlas for later use
[myAtlas preloadWithCompletionHandler:completionHandler];