(@[email protected], let me know if you have a problem with posting links to vendors in here. Since this isn't Reddit, I figure it's fine as long as it isn't for self-promotion, but let me know and I'll remove it and/or just add search terms instead of linking directly.)
I prefer to buy at a brick & mortar store so I can support local businesses, but I haven't found one with much selection locally (yet). I'm in the metro Detroit area (Michigan, USA), and there is a local chain called "Wild Bill's Tobacco" that has a few Ashton blends that I like, but their selection is only around 10 blends total, half of which are bulk.
SmokingPipes.com has a very large selection, and I have already put in my second order there. I'm finding that I'm partial to Virgina blends, but it's still early days on my pipe journey, so I haven't purchased anything larger than 100g (3.5oz) yet.
Note that they also have a large selection of pipes there. I picked up one by Erik Nording for < $50 that I really like, though you can spend a LOT more. (They have a filter so you can filter out the really high-priced ones.)