Midwest Basswood is often sold in art stores (even here in Malaysia, I've found it next to the balsa and plywood in art stores). Problem is you still have to strip/sand it to size, I suppose. If you're looking for another wood heavier than balsa there's also Paulownia - Daiso (Japanese "100 Yen" store chain - they're all over the world now) carries sheets of it.
A2Z is out of stock on this, so did some hunting and found out that Midwest makes it for architectural modeling. Dick Blick sells it but the shipping makes it expensive and they do not have it in stock.