I tried to type in 5.6 (five point six pp) but the system took it as 56pp, sorry for the confusion. 5.6pp is price at Cha 88; 6.4pp at Cha 57. Terman Underbelly, the merchant that sells this is in Underbelly's Arms, is at loc neg 418 x neg 116.
To find this in Thurgadin: after zoning in from GD and going over the bridges, take a right at the first intersection. Go into the first building on the right and the dorf on the right has it.