For anyone interested in this subject an update, we found a workshop! Yesterday I visited the TongZhi dragon kiln in Yongxingzhen, south of Chengdu. A very interesting place, they make a large variety of pottery with different techniques and still fire in the typical dragon kilns. You can also go there (alone or with a (school) group) to try to make your own pottery, decorate porcelain vases (specially made for this purpose only), or just to watch the experts shape and fire their pots. PM me if you are interested in the details.
We contacted the GuiHua town workshops but they were very reluctant and seemed not to be interested in a visit from us.