I don't buy LCG packs locally at all. The prices are outrageous - some LotR LCG packs are £20! Three at a time from Miniature Market is just right. Below the customs limit, so no VAT, and it's the largest shipment which is still within reason for shipping costs. I get 3 packs from the US for less than the price of two packs locally, shipping included.
As for how soon they're available it really varies. My FLGS is bloody useless. The website has some lower prices, but it's only updated whenever the guy who does that can be bothered. In most cases new, major products aren't even added to the front page, or even the product list. Dominion:Dark Ages didn't get a single mention, even though they dedicated a whole table to it when it finally arrived.
Typically the best way to get them to have a new pack in the store within a week of US release is to order it from the US. They'll have it a few days before my order arrives, without fail ![]()