If you're just looking for a handbrake for use only in GT5 then you can build one cheap and easy. You will need a controller (came with your PS3), a piece of string and a handle you want to use as the handbrake.
All of these things are typical things you might find around your house

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NOTE: I haven't tested this with other games so be aware

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First put the controller somewhere it will not move, even if you pull back on one of the analogue sticks. Then tie one end of the string to one of the analogue sticks. Tie the other end to your handle. Make sure the handle can't fall over but you are still able to pull back on it (you might need a pivot system for this). And there you go your cheap and easy handbrake for GT5 is finished.
When using the handbrake for the first time, you will need to make some adjustments to the controller assignments. If you tied the string to the right stick, then set the controller assignment for the right stick to be the handbrake (you pull back on the stick so you will need to set it to activate handbrake when you pull it). If you tied it to the left, do the same but with the left stick.
The last thing you need to do before you can use your handbrake is to set the controller to be "Player 1" and your T500 to be "Player 2". Doing this will make the game think that the T500 is still player one but the controller can override the wheel. If you don't know how to set the controller to Player 1 then hold the PS button on it for 1 second and then go into controller settings.
That's it. You are ready to use your handbrake. And what's good is that it is wireless so you still have one USB port free. You just need to charge the controller from time to time.