You have a part listed at Amazon.com here:
http://www.amazon.com/TerraTrike-Dual-C ... B001FYEOIE
... "TerraTrike Dual Control Brake Lever".
The product description says that it has a push button for a parking brake.
Thinking I would buy direct from TT, I tried to find it on your web site, but only found a dual lever <without> the parking brake.
Before I order from Amazon, would it be possible for you to VERIFY that the lever in question has the integral parking brake. (I already have one without.)
I'm also curious whether you stock the lever in right and left hand versions.
Alternatively, if you can suggest a way to order it from you online, I'll buy direct from TT.