A. Parker and Son's
The shops biggest claim to fame is that it received the first letter from the newly re-formed Ankh-Morpork Post Office, delivered by the Postmaster hims'elf. Admittedly the letter was written 41 years earlier by Agnathea to Antimony Parker accepting his' offer of marriage.
1 The Parker's not only use a great many apostrophe's (as befit's their trade), they have the unusual ability to pronounce them.
Antimony Parker was played by Matt Devere in the Going Postal miniseries.