I've never seen a valve or vale extender with a smooth bore. The closest I've seen are Zipp Tangente extenders, but even these have a knurl in place of the thread. I think you'll have to get different extenders with a thread at the tip, like these.

I have never had much luck with extenders in the past. I only run 80mm tubes on my 60mm rims. You can buy tubes online in bulk for far cheaper than in most shops. I generally buy 10-12 at a time and they cost $4-$6 each even for 80's