Yep you can definately still buy them all. Since VV3 was made to be the best out of the series, and it was made from changing things that people didnt like from number 2 and 1, you will probably like number three the best.
But, Virtual Villagers 2 is still great! It's got different collectibles, technology, puzzles, clothing and a different map. If you love the third one, I can almost guarantee you'll love the others.