See also the Antenna page. There are many manufacturers of toroids and we have no relationship with any of them.
A couple are listed here but a web search will turn up many more. Toroids can also be purchased through Amazon and eBay.  Be aware that if a balun is needed between the Twinlead (balanced) and the Tuner (unbalanced) a Current (a.k.a. Guanella) balun should be used, not a Voltage (a.k.a. Ruthoff) balun.
Most of these can be wound using #14 insulated “house wire” from the hardware store, if no special magnet wire is available.  #14 will theoretically handle over a KW but I would suggest not exceeding 500 watts.  Use two cores cemented together for more than 500 watts.