I got mine direct from USNO. They were kind enough to send it to me on DVD (gratis!) on an email request, when I explained the project I was working on.
Hi Ivan, I have been trying to find were on USNO site to email them to request UCAC 3 or 4 but no luck, can you remember where it is, I would really appreciate some help.
Note that anyone who has the Database Add On for TheSkyX also has the entire UCAC3 database in the UCAC3 sub-directory. The only file in the UCAC3 sub-directory that can't be redistributed is SB's proprietary subset plot file "ucac3 subset.plot". The rest of the contents of the UCAC3 sub-directory can be redistributed in its entirety so long as no fee is charged for doing so.