The Digital Print Shop is NOT AVAILABLE TO ALL STORES. Only the big stores or stores with potential to make money from these services have them. My local PC World in Staples Corner London have these photo printers. The staff who man these printers are the ones who are in the Digital Photography section. That could be one reason why no one seems to know which stores have this service
On one occassion I have seen someone printing a large family portrait and the quality was superb.