It is difficult to locate information on Grand Unions. Here's what I can share: The Tram Museum in Critch, England had one in storage as of May 2003. ntm_library at online dot rednet dot co dot uk per Ms. Marchant. Good GU pics appear in Traction & Models Nov 77, Jan 76, Nov 67 (pg 24), Railroad October 1943 issues. The best disussion of them has been in the Paul Mallory Traction and Track Handbooks. I've had several built over the years in HO scale using Richar Orr (Omaha, Ne) girder rail, but they don't come cheap. I also got excellent cooperation from the Toronto Transit Authority who sent me drawings. I wish I could say the same for Chicago CTA. I believe there's an excellent pic of one at Trenton NJ in the August 77 T&M but as I write this have not been able to locate my copy to confirm. It's somewhere in my railroad library.
I'd also refer you to the treatment done at [www.pitt.edu
I understand there are special trackwork catalogues such as 1912 Barbour-Stockwell and one by Wharton Co., but they are extremely rare and difficult to find. The 6-way union featured in the Oct. 43 Railroad pic was built in Buda shops, outside Chicago.
One letter I received from Bill Olsen of Mpls states, "There are two types of grand unions: One with fixed raii curves...the other with compound curves go give car clearances for narrow @#$%& strips." whatever those are.
The only commerical manufacturer of Grand Unions of which I'm aware was LINDtram, P. A Lind, Box 512, 701 07, Orebro 1 Ban, Sweden. They advertised in T&M in the early 1970's.
Hope that helps.