Currently, there are only two sources for reproduction Civil War bugles.
The only musical instrument maker that was making period-correct Civil War bugles was Amati. However, they went out of business, so look on eBay for the following:
Amati ABG201 Bb Bugle
It is a Model 1839 French Clairon brass bugle used during the Civil War and can be tuned. It comes with lacquer, so you will need to have the lacquer removed. This horn sounds great, though. The clairon bugle was also the most widely used bugle during the Civil War.
If you can't find an Amati bugle, then you can order the next best thing from the Civil War sutler Jan Berger in Germany. He makes a copper Civil War bugle in the key of C with a Bb pigtail crook. He is a reputable bugle maker. His horns sound pretty good, but they are not tunable.
Here is the link for the Berger bugle:
His email address is as follows in case you want to find out how to order one and how much they are in US dollars.