To Nordfrim's credit, the quality is quite high, often "bank mix" type quality. They're not like the old foreign mission mixture cloth bags offered in US variety and department stores that had extremely common stamps, each salted with one or two faulty high values. Even as a kid, I thought they were picked over already. Cancels and varieties could be found, but how many of the same Canadian, Indian and Ceylonese definitives could a body want? Still, you probably got what you paid for including time spent. The bag was useful.
Turntostone, I'd set up searches for individual countries (as "used" or maybe "modern used") as well on eBay
for notification. Sometimes small lots or groups of covers will show up. Of course, that means wading through lots that might not be useful to you. If you only want stamps from the last year or two, that is a much tougher thing as you've probably already found out.