Check western tack retailers- western reins are usually quite a bit longer than english, and if you're just pleasure riding at home or something, the eight-foot or nine-foot split reins might work for you. I love them.
I bridge mine (criss-cross them over the horse's withers so each rein hangs over the opposite shoulder), and ride as if with normal joined reins! The bonus is that if you have a balky or lazy horse, you can take both reins in one hand, and use the end of one rein behind you on the horse's hindquarters (like a crop, but as you're just using a rein, you don't have to carry anything extra- I don't like having too much in my hands, so it's quite convenient). With my horses, all I have to do to get them to move forward (if they're balking or ignoring my nudges and clucks) is dangle a rein out just within their view- they know to either move forward/speed up, or to expect a little tap on the rump.
If you plan on jumping or doing any fast work, knot the reins- it's quite possible for you to lose a rein, but if you drop one, it's gone- very very dangerous. Not only will you have limited control of your horse, he could step on it and pull himself down. Also, if you plan on doing any competing, they might frown on the long split reins- lol.