It depends upon what type of intestinal permeability you are looking for.
If it is Protein e.g. album loss , then alpha 1 anti-trypsin clearance in a 24 hour stool can be measured. PLE is also diagnosed by Tc-99m albumin scintigraphy (99mTc-HAS). I would search NCBI data bases for intestinal permeability tests, find what type you want (protein, fat, CHO) and then go to article and email corresponding author to describe which co-author did the testing. Authorize the corresponding author to forward you email to that person so they can initiate contact with you. They are in best position to know how to find you the optimal collaborator (proximity, best, etc)