Hello
You may find ICAO holding speeds at the Jeppesen Airway Manual on the "Air Traffic Control" section. There you can find the ICAO and FAA holding tables.
At the end of this section, you will find the slight variations in air traffic control that every country has (including the holding speeds).
The number of countries listed there will vary according to your Jeppesen Airway Manual coverage (North America, South America, Europe, etc.).
Hope it helps
Antunes