This is were I bought it from. http://www.amazon.com/HICTOP-Desktop-Accuracy-Self-Assembly-Tridimensional/dp/B00N7I1ZVU
Assuming your electronics are open source (such as RAMPS), you can buy upgrades and spare parts from pretty much every 3D printer spare part provider out there, as long as they suit your needs and the specs of your printer.
In other words, if you want make a headbed upgrade, find some bed that i.e.:
- Fit the size of your printer
- Can be mounted properly
- Can be used with your current electronics (and possibly software)
In general, most DIY hobby desktop 3D printers today use more or less the same components mounted in various ways.