I usually preface with a phone call to the relevant cad document purveyor (Arch,Mech,Struc), and follow up with a requisition letter via e-mail, listing all the files I need. Most of the smaller firms are happy to help, but I've been noticing lately that quite a few of the larger, national and international firms are starting to charge (a) per drawing or (b) a flat rate for any required files.
If that's the case, I usually dump it on whomever we're subbed to, be it the plumber/tin basher or general contractor. They usually have a bit more weight to throw, and since I always write it into our standard bid letter that we require electronic files, they usually take care of business pretty quickly.
Of course, this is all on the assumption that you're a sprinkler designer looking for floor plans to lay out your system.