Folder Reference または bundle resource のなかにある画像をimageNamedでとってくる方法

答え:
ふつうにフルパスを書けば良い

[UIImage imageNamed:@"path/to/file"];
[UIImage imageNamed:@"bundleName.bundle/Contents/Resources/file"];

もちろん

NSBundle *bundle = [[NSBundle alloc] initWithPath:[[NSBundle mainBundle] pathForResource:@"BundleName" ofType:@"bundle"]];
NSString * path = [bundle pathForResource:@"file" ofType:@"type"];
[[UIImage alloc] initWithContentsOfFile:path];

でもok