Since Mt Lion was released the only way to buy Lion was to call Apple sales and buy it over the phone. Apple will then send a Redemption code to your Apple ID email address that you can use in the Mac App Store to redeem, download and install Lion. At least that was the way it was.
But now since Mavericks is a FREE upgrade they might of stopped selling both Lion and Mt Lion. The only way you can get either of those 2 previous version of OS X was from the MAS and to do that you needed Snow Leopard 10.6.7 or .8. Now if you have SL 10.6.8 you can get Mavericks for FREE. If your Mac computer can't run Mt Lion or Mavericks then Apple might just hang you out in the wind. Figuring IF you hadn't bother to upgrade an OLDER Mac to Lion, one that can't run Mt Lion but can run Lion (Lion has been out for over 2.5 years now), it's time for you to buy a new computer. Apple stops all support for their computers after 5 years. So if you have a early 2007 model you are stuck with running whatever version of OS X is now on it.