Almost all of my online HA purchases have been via eBay, Amazon, and Monoprice (in order of most-least).
Physical stores it would be Lowes, Target, and Home Depot (with not many at any of those).
As for the GE Switch you mention at Smartthings... I was trying not to mention it directly but Smartthings is pretty open ended, so any device that works on them is likely an open-communication one and can work with an Almond. The main difference might be that Securifi might need to do a bit of work if it is not there, for specific features, but for most general features (on/off switch, dimmer, etc...) the basics will be fine.
That GE Switch is model 45856GE (also sold on Amazon, but for MUCH more than your link). GE-branded products are pretty open (I have multiple different ones). I found one store cheaper ($3, so nothing huge at this cost) and who knows about shipping, but here is the link:
http://shop.haworldonline.com/GE-ZigBee-In-Wall-Smart-Switch-Model-45856GE-ZB4001-11405.htm