The short answer is that you can already TWF with two reach weapons - if you can wield a reach weapon in each of two hands.
In addition to what others have suggested, you could buy two weapons one size category smaller than you are (for example, if you are medium, buy two small spiked chains). This makes them one-handed weapons, but you take a -2 penalty to attack rolls with them (in addition to the penalties from TWF) and also decreases the damage die. The attack penalty, on top of the costs of TWF, is annoying, but the damage decrease is compensated by the fact that you're wielding two of them.
Because of the extra penalty and the lower damage, I would really only do this if you didn't want to be aberrant or deformed, and you couldn't get access to any reach weapons that are naturally one-handed.