I personally think that Trade Shows are a great way to find developing markets, but you need to have a budget behind you to source this way as the suppliers are there looking to develop serious business relationships, not to be bothered into selling a dozen units.
I don't personally know of any trade show calendar, however someone else may well have some information on that in the US.
Regarding wholesalers that are not online, who knows what the numbers are, but I would suspect that most wholesalers aren't actually online to be honest.
Take a look at local business's around your own area, just because they may be the manufacturer doesn't mean that you may well not be able to source wholesale through them direct, will just depend on their distribution structure, but always well worth sticking your head in the door to find out if you find a product of interest being made nice and close to you.
There has to be so many opportunities like this getting missed by so many because no one wants to leave the computer anymore, most just want to sit in front of the PC to do everything, source and sell product.
I find all my deals offline, at least 90% of them, and that's because I am looking where there are limited buyers competing, that's not the case sourcing online, you are trying to source from suppliers who have thousands of buyers all trying to by and sell there products.
Of course you can source good products online to sell, but if you are not searching offline as well, then you are simply limiting your supply avenues.
As for finding an Asian Sourcing Agency, I have no one specific in in mind, but if you do a simple Google search, something like, finding a Chinese Sourcing agent, you'll get a stack of avenues to explore.
A sourcing agent can be a very effective way of doing business through Asia, especially China, however you need to research that the company you choose is completely independent.
What can quite often happen is that you will find a company that is essentially marketing their own products under the banner of being a sourcing agent, so in that instance you aren't going to get much of a choice.
Of course most agents have working relationships with manufacturers already , and that's what allows them to get you a solid price in the fist place, but just make sure they offer you options so you are the one who can make the decision on who, and how you do the deal.