The original Diskless-HOWTO mentions the names of the following vendors of diskless computers:
Linux Systems Labs Inc., USA http://www.lsl.com. Click on "Shop On-line" and then click on "HardWare" where all the diskless computers will be listed. Phone 1-888-LINUX-88.
Diskless Workstations Corporation, USA http://www.disklessworkstations.com.
Unique Systems of Holland Inc., Ohio, USA http://www.uniqsys.com