I don't think it's possible due to the sandbox nature of apps meaning that the required information isn't readable. I can't find reference to any Apple collated list either.
This quote from the Apple Docs, though not conclusive, implies that it's not possible since it's not even possible to determine which app, if any, will open.
**Note: If more than one third-party app registers to handle the same URL scheme, there is currently no process for determining which app will be given that scheme.
If you already know which apps you want to check are installed, this method should return YES:
[[UIApplication sharedApplication] canOpenURL:[NSURL URLWithString:@"myScheme://"]