Define "large slow-acting". That's not a clear technical description of a diode. Do you mean physically large? Slow to turn on? Slow to turn off? What are you trying to do with these diodes?
Some diodes are called "high speed." They are placed in circuits where a high frequency signal is present. If you use an "ordinary" or "normal" diode in this type of circuit, it gets very hot. Some high speed diodes are RED but in most cases you have to read the specs data to determine if they are high speed. High speed diodes are available as junction diodes and as zener diodes.