thanks to Tom Hawley of Michigan Models <firstname.lastname@example.org>
The GP-35 is made by American Models of South Lyon Mich.
Their web site is http://www.americanmodels.com/
On their home page click on Locomotives, then click on GP-35,
Note you can also back up one step and find the ALCO FA-2 locomotives.
S scale decals for doing your own Ann Arbor GP-35 and FA-2 are available from Des Plaines Hobbies.
Their web site is http://www.desplaineshobbies.com/
You will find their S scale decal AA-1 for the FA-2 locomotives, and decal AA-2 for the GP-35.
The composite hoppers in Ann Arbor markings are made by S Helper Service of New Jersey.
Their web site is. http://www.showcaseline.com/
There will soon be panel-side hoppers marked Ann Arbor, but they apparently haven't put those on the site yet. NOW HERE
CDS Lettering also has AA Decals