Dispensationalism is big word used by some people to describe people that "Rightly divide the word of truth". I'm sorry to say, but you will run across other big words like hyperdispensationalists and ultradispensationalists. Don't let these bother you. Some people use these terms to describe people that rightly divide the word of truth but differ on different issues like when the church the body of Christ started. All these big words are based upon pride. Always remember the bible says, "Knowledge puffeth up, but charity edifieth".
The apostle Paul used words that were easy to understand and so should preachers and teachers of God's holy word.
The bible talks about them that "believe and know the truth" and that is how I prefer to be known, as a plain old everyday bible believer. Even though I rightly divide the word of truth as others at this forum, I do not claim to a dispensationalist, but rather just a bible believer. The apostle Paul never claimed to be a dispensationalist, but just a simple believer with a special message of grace.
But anyway, to answer your question, dispensationalism is not a denomination but rather a belief. The apostle Paul received a special doctrine of grace from the Lord Jesus Christ, and was told to preach it unto the Gentiles. These teachings were passed on to Timothy, Titus and many other fellow laborers in Christ and passed down through the ages until this present day. So if you want to, you could say that it was started by the apostle Paul sometime during the first century. As far as I know, all the preachers that teach this grace are independent as was the apostle Paul. There is no denomination. The Lord never made denominations. Man did.
Personally, I cannot belong to a denomination. Why? Because denoninations cause division among the body of Christ. Denominations speak different things, they believe different things. In 1st Corinthians it says we should, "all speak the same thing and let there be no divisions among you". So true believers should strive to speak the same thing, but there is a lot of division among the body of Christ. I wish I could do something about it, but I can't.
You will not find a headquarters for this so-called dispensationalism, because none exists. But I do encourage you to continue to seek the truth. People that really want to know the truth are very few and far between, and it really excites me to find someone that is really seeking the truth. You are a rare breed.
My name is Jerry Pourcy and I am the pastor of Grace Bible Study. We have just started our own website and though we don't have a lot of features up and running yet, we have a forum along with a live chat room that is operational. I will be more than happy to discuss the bible there with you. On our site we also have links to other grace sites that might be helpful to you. If you are interested check us out at http://www.gracebiblestudy.net
Like you, I just so happen to stumble across this site. I find it interesting, so I'll probably come back to it again.
Once again, I don't know how you came about your beliefs, but I do encourage you in continuing to seek the truth. Once you see it, it will open up a whole new world of understanding.