Other than the "lottery" which is unopened bags(not likely to contain anything better than dinkers, maybe a YB), you'd have to be in contact with the exporters in africa.
The exporters are not idiots either. They don't hand over a new morph for nothing. They probably tend to favor whoever it is that gives them the most business. So people who import a lot of stuff fromt hem are more likely to get offered something new and special.
If you just want some nice normals, or poss dinkers, you can buy from people who import. Yes, there is a mark up, and yes they can choose to keep anything that looks exciting to them, but you can always spot something that YOU think looks exciting.
I'm pretty sure a lot of the subtle morphs were just dinkers when they first showed up. The breeders that got the first yellowbellies probably were told "Nice dinker.. probably nothing" more than once, for instance.
Just my opinion.
Added:
I'd bet for every project that pans out into something cool, there's ten that turns out to be non-genetic. Just guessing though.