You might consider contacting Joe West at U of Nottingham as a "local" researcher who has used vendors/suppliers for ATG Abs 

Samples positive for EMA were tested for IgA class human anti-tissue transglutaminase antibody (TGA) by using human recombinant antigen in a quantitative enzyme-linked immunosorbent assay (ELISA) kit (Celikey; Pharmacia Diagnostics AB, Freiburg, Germany). At a cutoff of 5 U/mL this assay has a specificity for celiac disease of >99%.

Address requests for reprints to: Joe West, BM, BS, PhD, University of Nottingham, Division of Epidemiology and Public Health, Medical School, Queen’s Medical Centre, Nottingham NG7 2UH, United Kingdom; fax: 44-0-115-8230464.

Hope you can get details from them if the have a newer , reliable, reasonably cost source 

Best wishes