ebay is you best bet or perhaps some open box at a B&M but I doubt you could find one as they have be out of production for some time.
I got to know why you want a HD-100. This is most likely the worst D* stb I have ever used. The HD-100 was extremely bug ridden (it use to drop out picture on the half hour marks) and did did not support AGP, e.g. the only way you could get local guide data was via PSIP and most stations do (or at least did) a very poor job at accurate PSIP data. The problems with this box were so bad that Sony actually sent me a check for $799 + Tax, buying this POS back. Oh, I almost forgot the fan in this box sounded an aircraft (yeah , yeah I know you could open the box and remove the fan but what kind of nut would do that).
The best and only feature that was worth wild was the variable mode where if you had a 4:3 hdtv and the station broadcast in 4:3 480i mode the HD-100 would output 480i automatically on the component cables. I have to say this was a nice feature for watching SD content, but unless you are using an old 4:3 TV most of todays STBs have better features like NLS modes to deal with 4:3 content.
Regards,
Brian