Online, you can buy through Amazon, but you will probably end up getting a
better price if you're willing to use
eBay. The eBay prices are frequently quite good in part because of people who find the retail sales mentioned below. If you use either of the links above, I get an affiliate "kickback",
so I encourage you to use them if you do buy Heroscape via Amazon or eBay.
eBay also typically has most of the expansions as well as the ability to by additional terrain piecemeal or the like.