At this point, this includes Alpha (many vendors), and a few vendors of PPC, MIPS, and ARM systems.
Some of these are not Linux system vendors, but this should be a fairly complete list of Alpha system vendors...
They specialize in numerical computing systems, selling Digital Alphas, and (in the past), things like Inmos Transputers and Weitek coprocessors. They produce their own family of FORTRAN compilers.
Resell used Unix systems, notably including Digital Alpha systems.
Great Lakes Computer Vendor of Compaq/Digital computer equipment, new, used, and refurbished.
Computers - San Diego, CA
These guys have been known to have remaindered Alpha boxes and Sun Sparc for sale.
This site has some decent links to sources of AXP support...
A European Alpha system supplier
A vendor of computers based on IA-32 and Alpha architectures, they sell machines with Linux pre-installed, including the "Aeneas Supercomputer" installed at UCI.
A StrongARM-based design from India intended to be the basis for allowing people in the Third World to have inexpensive access to computers.