How to book internal flights from outside

I've already written something on this and have now tried several internet options all without success. The situation is probably a common one for any single traveller wanting to get to Western Mongolia within a reasonable time: by land is expensive and takes a long time and is a pain in the butt - OK if you have a big butt I guess. Otherwise you want to fly. The problem here is booking an internal flight from UB to the West from outside the country. Trying to get a flight on arrival is most likely not possible within the one month visa time frame in the summer months and one airline has recently had its license cancelled due to safelty concerns. How many airlines are there? The airline websites I've found don't allow for online booking of internal flights - and it may not work even if they did. Tour agencies don't respond. My guess: not enough profit in it unless the person is signing up for one of their tours. The guesthouse I stayed in last year - the much touted Golden Gobi - and another person I contacted in the west through email avoid the issue and promote their tours instead. That's where the money is.
Any ideas anyone?