I bought one in the Fall direct from Mayfair Games. I would call them to see if they still have any.Personally, I would prefer cheaper (around $20 AFTER shipping), but if I HAD TO buy one today, given it is OOP, I would go for that.
Edit: I just checked their website and they still have them for $20.00.
If you're feeling desparate/adventurous, you could succumb into DIY mode.
RULES - 3rd edition Mayfair SoC ext should still be available online
BITS - if you go to a convention or board gaming store, they sell spare parts that you could buy up for 5 to 25c each
TILES - that's gonna be the most difficult. If you can buy spare copies of Settlers base game, or buy incomplete sets, that would hold you over.