I'm pretty sure it's this:
www.acurapartswarehouse.com
A heads up though. Mine is kinda flaky so I tried ordering it from two different places and both said the part is discontinued. You might have to looks for junk parts or rig in your own switch. Or if you want it permanently on, you can probably short the wires together or something.
35810-SEC-A01 Genuine Acura Trunk Opener Main Switch
Genuine 35810-SEC-A01 Trunk Opener Main Switch fits 2004-2008 Acura TSX. AcuraPartsWarehouse offers 35810SECA01 for $43.77.

A heads up though. Mine is kinda flaky so I tried ordering it from two different places and both said the part is discontinued. You might have to looks for junk parts or rig in your own switch. Or if you want it permanently on, you can probably short the wires together or something.