This page contains links to web sites dealing with Toroids.
There are many manufacturers of toroids and most of their websites contain winding information about their toroids, allowing easy calculation of the number of turns required to achieve a desired uH value. Not all manufacturers will sell retail quantities but their products are available from many retail outlets such as Mouser, etc. Here are some sources:
Micrometals Iron Powder Cores
Fair-Rite Many Ferrite products
Amidon (a distributor of Micrometals and Fair Rite products) Both Iron Powder and Ferrite cores, as well as handy calculators.
About Copper Wire and Toroids: Much useful information about wire and toroids is presented here, by KC9RG. It’s an excellent resource.
Using Toroids in Tank Circuits – a most informative article.
Here’s a handy toroid calculator.