The following links help with finding sheet music, research findings on the voice or online ear training:

• Complete Vocal Institute
  Information about the method, training possibilities and research about the voice (in English)
• Theta Music Trainer
  Lots of amusing and interactive ear training games to test and improve one’s ear and musical knowledge (in English)
• Sheetmusicdirect
  Order music online or print out directly. Affordable prices
• Sheetmusicplus
  Order music online or print out directly. Affordable prices
• Musicnotes
  Order music online or print out directly. Affordable prices
• Les Arts Scéniques
  Martina Rick’s theater group & school: performances, acting classes and more