I remember writing to SDI about two years ago, asking some questions about Inner Space and they gave me a prompt reply at the time. So I naturally found the comments made by BugMeNot quite interesting.
I thought I'd plug an email to their sales department asking if the game was still available and within 45 minutes, I got a reply saying they still sell it. It is not likely to be an automated reply, because it contained some minor syntax errors, not to mention that it sounded much too personal for an automated template. Clearly there was no email bounce though.
For now anyway, the conclusion is inescapable. This game is simply not abandonware, as much as we all wish it was
I don't know how much hope there is that the author will release it as freeware either. Even if he wanted to, sometimes authors have made previous agreements with publishers in this kind of situation that prohibits them for doing so. It all sounds rather dismal to me.
By the way BugMeNot, the site states that it's not possible for them to sell the add-ons alone, you have to buy the full game from them too. That might explain why you had trouble receiving the add-ons you ordered