Thermac Replacement?

[chevymotocross]

I have an 87 silverado with the 305 TBI engine. I notice that the flapper in the intake is not opening when the engine is warmed. The duct running from the right-side manifold, to the flapper on the intake is fine.

This has the "wax pellet" type thermac, not the vacuum operated kind. When I go to parts stores, everyone looks at me like I am from another planet when I mention this. I try the internet, and I notice none are listed at the parts stores websites.

Do they even sell these anymore or is this a junkyard piece? Can I keep it open with a zip tie or mechanic's wire for now?