Hi Ms k
Try call to Consulate general of Japan in Chicago and Ask for JETRO phone number. JETRO, short of Japan external trade organization which is goverment private cector working togather to promote Export,Import of Japanese campany and forgin company. They have huge data for Japanese campanies. Consulate General of Japan has small amount of such data, and most of time they reffer to JETRO. When you call JETRO, try to talk Japanese officer. Many American working to assist many request of informations. American worker may not know anything you are asking for.
Also kyoto Chamber of commerce and Koyto Zoen kumiai is good place to call. If you can find any well know Japanese garden Archticts, he may know where you can find Goboshi/Gihoju.
Try to use botanic garden letter head and name .
I have few peoples names I can think of.but You try first your self. If you can't find ,let't me to know.

( I'm busy too and cost me many hours and money. after you spend your time and effort and still can't find it then I will help you.)

Giboshi is not item of mass production. It made by "bankin ko" sheet metal craftman.......I think.

Japanesegardener1@yahoo.com This is my email address. Send me email, and let's me to know what is the specifcation, number of quantitiy etc.
..........Yama