I have used Nichols Diagnostic which may now be called Quest Diagnostic for assays on mouse plasma ACTH levels and it worked great.

Thank you James. Do you have a product or catalogue number? I can't find it on their website.

We have used:

ACTH RIA kit, Cat. No. DSL-2300, Diagnostic systems laboratories, Webster, TX

You can refer to our article in SYNAPSE: 61:561–568 (2007) 

Sex Differences in the Regulation of Cocaine and Amphetamine-Regulated Transcript Expression in Hypothalamic Nuclei of Rats by Forced Swim Stress

OGUZ GOZEN,1,2 BURCU BALKAN,1,2* GORKEM YARARBAS,1,2 ERSIN O. KOYLU,1,2 MICHAEL J. KUHAR,1,3 AND SAKIRE POGUN1,2

You could contact to Dr. Parlow group at UCLA. (NATIONAL HORMONE and PEPTIDE PROGRAM). They developed kits for a lot od hormones (human, rats, mice, guinea pigs, etc.). We used their rat PRL RIA kit, and antibodies for all pituitary hormones  for immunofluorescence.

URL: http://www.humc.edu/hormones/material.html

Thank you, Daniel and Sakire. I will look into these sources. The humc source looks particularly promising.