Is there a Stack Exchange site where these two questions about where to buy programming related products would be on topic?
I really don't think any site on the Stack Exchange network would welcome such questions.
The first one is, in my opinion, clear-cut: "best" is subjective, and the answers would be likely to degenerate into a list of vaguely spammy links to everyone's favorite online store.
The second has the merit of being a bit more specific (looking for something in a specific area), but it's still fundamentally a meta-shopping question (selecting/finding a shop rather than a product), and I don't see how that could fit. (See: Q&A is Hard, Let’s Go Shopping! for the shopping part.)