Don't beat yourself up on that account. James H Schmitz and Eric Frank Russell have been dead for 30 years, and J T McIntosh (a pseudonym for James Murdoch MacGregor) stopped publishing SF at around the same time, although he only died in 2008. The one whose books you were most likely to have met was Schmitz; following the efforts of a bunch of his fans (of whom I was one 
) all his stories were republished in roughly 2000. You might still be able to get the updated stories from Baen Books. The Russell & McIntosh stories are much rarer, and the best source is probably at the link below.
