Most of the Alpha motherboards sold today go through Samsung and API NetWorks. Samsung handles some of the sales for Asia where API NetWorks, Inc. handles the Americas and Europe.
In general, it's likely that buying a complete system will actually be cheaper than putting one together yourself. This is especially true for many of the third-party systems and for Digital's XL machines. If you add the costs of all the components to the price of the motherboard, you'll quickly find that it's difficult to beat those prices. The good news about this is of course that it will also save you the trouble of having to find appropriate parts. A number of third-party vendors can be found through the AlphaPowered page. They typically offer configurations based on 164LX and 164SX boards, but some may have nice deals on the older boards as well.
Linux will also run on some of Digital's server-class systems. Check the table in the previous chapter.
A brief (but unfortunately rather dated) introduction and overview of various Alpha systems and processors on the market can be found in Brief Alpha System Overview.