Through a bit of creative Googling, I was able to find the travel agency's web site:
http://www.cnctrip.com/service/agenc...es.asp?id=2929
Assuming the flights are still on offer (questionable since summer is over), since they are technically charters, I think that travel agency may well be the only booking channel.
The morning MU flight isn't a horrible option though because it only spends 45 minutes in Kunming. On the other hand, I've never once seen it discounted. If you don't mind the hassels associated with connecting (i.e. you'll likely have to check-in a second time), you should be able to knock up to 40% off the fare.
For example:
direct flight
PEK-LIJ: 2410 + 130 = 2540 ($339)
mannually constructed connection
PEK-KMG: 910+130
KMG-LIJ: 410+100
=1550 ($207)
That's a 39% price difference. However, it's worth noting that I picked the two cheapest flights on a random day in order to pull off the connection case. If you want a nice connection, you'll probably have to pay an extra 100 or so for each segment, but that's still $100 cheaper than the direct flight.