ReamerRentals.com has the 357 B&D reamer available for $39.

The plastic sleeve thing was for a completely different concept. That one involved a 44 mag cylinder fit to a 357. The sleeve filled the chamber space. G&A magazine did a cover story back in 70s or early 80s.

When done right, the 357 B&D is actually quite good, especially if done with a matching die set. Everything is to close tolerance and the long range accuracy is really good!
One big advantage over the 357 maximum, is you get it in a very reasonable sized package that's easier to carry and shoot off hand than a huge Ruger SRM or Dan Wesson.

As another person posted, it's at it's best with heavier bullets.

I hope you give it a try!

Jim