It is the retailer who is responsible for sorting the warranty and not the distributor.
Yes and no. The retailer is responsible for meeting their obligation under the sale of goods act. This means that if it is “not of satisfactory quality” then it is the retailer who has to deal with it. The period for which you can do this is not explicitly defined, and depends on the “expectations of a reasonable person”.
Manufacturers typically provide their own warranty in addition to your statutory rights, which gives you cover for a specific period (e.g. 2 years). The procedure for returns under this warranty depends on the terms, but is typically “return to any authorised dealer”.
If you find that the terms of the manufacturer’s warranty aren’t being honoured (e.g. because there’s no distributor to get spares) then you might reasonably be able to claim a refund or replacement from the original retailer on the basis that it doesn’t meet the description of having a warranty.
One advantage of returning under the SoGA is that you’re entitled to a partial refund if the repair or replacement takes an unreasonable time.
Whichever way you look at it, SS selling seatposts when they know that there’s no distributor is more their problem than it is yours 😀