Man, Dave i wish I could remember where I saw some one having those in bulk. They were the black ones like Estes used for the last Sterling kits. I searched eBay but found nothing. Maybe contact Estes and see if they have stock remaining? They sell rockets kit parts in bulk  so if they have them on hand they may be receptive to selling some.

   Do you need any handles?  I have accumulated a lot of the Cox RTF handles over the years. let me know , send me an email I can send photo to and I'll send you some pictures.

  Type at you later,
   Dan McEntee

 If I ever saw an ideal application for using a 3D printer this would be it. 

Dan: We have lots of the hollow red plastic handles, but the kids like the one shown in the photo better. Easy to adjust. If you have any of those (any color), I will give them to the kids. Thanks!

       The red ones you mention are probably the Goldberg handles? I like the shape and feel of those but they are fragile, and with kids being kids, if you step on one, it's finished!! I hope to dig out that box today and will get back to you.
       Can you PM me an email address I can send pictures to? I can email you some photos of what I have.
  Type at you later,
   Dan McEntee

Even 1/8" tomato crate wood...it's only 1/2A. A reasonable Cox facsimile could be done.

As for the handles, got some 1/4" plywood and a jigsaw?

Why not go really old school?  Grab a wood broomstick and cut down into sections, then drill holes in the ends.