At the moment, sourcing (shopping) questions are discouraged at Electrical Engineering. Many shopping questions are of low quality. For example, the author didn't do enough web searching.
On the other hand, some sourcing questions make good forum content:
O.P. posts his research/homework. E.g. "I could only find these, but they don't quite fit the bill, because [...]"
Sourcing is very important for those who do hands-on work. If somebody doesn't have the right stuff, they get stuck.
Sometimes, the sought item is antique, exotic, or non-existent. Such items are difficult to look for and peoples' opinions help a lot. EDIT: Besides, sourcing questions of this particular subspecies have a tendency to evolve into more academic discussions. E.g., what had superseded an antique, why it doesn't exist, and so on.
EDIT: Sourcing questions can make good wikis. For example: aggregate list of electronics suppliers.
My point: If we make a privilege for shopping questions, we can encourage high quality sourcing questions.
P.S. Sourcing questions are not at all discouraged on major electrical engineering forums (such as: edaboard.com, forum.allaboutcircuits.com, dutchforce.com).