None of the listed are being sold anymore. You'd have to buy Lightroom 5, or Lightroom 6 when that comes out, eventually..
Which operating system are you running?
Given the (old) age of the version numbers you're quoting, it's possible that your operating system may be too old to run Lightroom 5 or 6.
So you may need a new computer before you upgrade your software.
Yup, I am in the middle of backing up files so I can upgrade my os from vista to 7.
You have several options open to you, choosing either to wait for the introduction of Lr version 6, which is due in the next month or so, or if you definitely want an older version, search for it on sites like ebay or Amazon, as Adobe doesn't sell v3 or 4 now. I should say that v6 will only run on 64 bit systems.