Just like any industry, whereever you can from multiple sources that give you a value added and profit advantage.

There is no one stop shop.

LBS, local big box, jeff bezos shop, other online giants that are national europe asia overseas, auction sites, aftermarket classifieds like cragislist, fb, varagesale, whatever.

I am an active bike flipper and I know there are other resellers from my hometown here so the above is as much as I'll say.