Thats not the way it works in Australia.
Yes, we have done ' A' tours in the past, but for the overwhelming number of our players, the transition is ...
Club -> State -> National side
Many - but not all - players get talent-spotted, and go to the Academy in Adelaide between Club and State, and quite often players go to England at some point (the Lancashire League was very very important to Shane Warne's career).
If I was in charge of Bangladesh cricket, I'd be on the phone to little towns in Lancashire, saying "We've got a couple of good young kids ... Shahadat is fast, and Aftab Ahmed can bat a bit".
The biggest problem would probably be fixing a visa for them.
Similarly, there are many clubs in Australia that would be happy to take a good young player.
The issue with an A tour is that it's expensive, especially if you want to go somewhere with radically different conditions, and it isnt likely to make money.
On the other hand, going one player at a time allows individual sponsorships ... Banglacricket could probably scrape up fifty quid a week spending money if, say, Aftab Ahmed ended up playing in Lancashire.