Gun shows do not provide gang members with large quantities of guns. Like was said, many times before, there is no gunshow loophole. There are private sales of firearms without the requirement of a background check, and also, in most cases a relaxed age restriction. An 18 year old, in most states, can buy a handgun from a private party, but cannot buy from an FFL.
What closing the so-called gunshow loophole would do is make it impossible for me to sell guns that I no longer desire to keep. Have you ever bought a car from a dealer? You know all the paperwork that you have to do to buy a car from a dealer? Can you imagine if you wanted to sell a car and you had to do all the paperwork that a dealer does? It's the same way with guns.
There are Federal laws that govern private firearms sales. Most are contained in Title 18, Chapter 44 of United States Code, Section 922, more commonly known as 18 USC 922. For your research I would recommend you download this:
http://www.atf.gov/pub/fire-explo_pub/2005/p53004/p53004.pdf
For instance, it is against Federal law for a private party to:
1. Knowingly sell a handgun to anyone under 18 years of age.
2. Knowingly sell any firearm to a person whose state of residence is not the same as the seller's.
3. Knowingly sell any firearm to a convicted felon.
4. Knowingly sell any firearm to a person convicted of a crime of domestic violence.
So, actually, many of the restrictions that dealers have regarding sales of firearms also apply to private sellers. Additionally, there may be state laws regarding the private sale of firearms that may apply as well.
Also, as stated earlier, licensed dealers at gunshows must conduct business at the gunshow under exactly the same restrictions as at a gun store, including all the paperwork and background checks.
Anyway, I hope this information, especially the guide to federal firearms regulations helps you out. BTW, when you are looking at the regulations, what you want to look for regarding private sales is when the phrase "other than a licensed dealer, manufacturer or importer" occurs - those are the requirements that apply to private parties.