I didn't use it when in Japan,('85-2010) but did use different lacquers. I agree with contacting Jonathan Brooks to see where he gets his.
www.carolinapencompany.com
I did contemplate giving it a try once but the fear of allergy and then the difficulty of finding an agent to purchase from on the uSA side was very difficult.
Urushi allergy:
"A true urushi allergy only affects a very small percentage of the population. If you have an urushi allergy, it will become apparent straight away, just by being in the same room where raw urushi is being used. Symptoms include red, swollen eyes, itchiness, and inflammation."
Since I have a strong allergy to poison oak/ivy and even some "English Ivy" sap, I have been hesitant to using it in the raw form. Once properly cured, it has one of the highest temp and wear resistants of most any other finish.
I do have an appreciation for their Urushi finished plates, bowls and other wood finished with it.