Sourcing in the EU
If you're located in the European Union, here's a list of shops where I got most of the stuff needed to build a SMuFF. Always keep in mind: Shops within the EU usually deliver all over Europe for reasonable prices.
The big advantage is that you'll have your goods delivered within 2-3 days, as long as they're on stock. Another advantage is, they don't suddenly disappear over night, hence, whenever you need spare/replacement parts, you'll most probably get them there, even years after - not to mention refunds or replacements in case something went terribly wrong.
Most of the shops listed here (in no particular order) do either have a local website (using domains like .de, .at, .nl, .fr, .be or .com in general) or, they at least allow you to switch to English language for browsing & ordering.
Disclaimer
I'm not affiliated with these shops in any way. I don't get any kind of commission or discount if you order there, so feel free to look out for a different shop/seller near you, you're most comfortable with.