"I'm curious if anyone knows whether Confederate prisoners were issued any clothing in these prison camps and were some of the items Union uniforms?"

In reading the book on Elmira, it is my understanding that "circular No.4" was a regulation that Hoffman wrote early on that all prisoners would wear plain gray. The war department provided funds for and did send some items for a time. The distribution or use of the funds was left to the camp commander. Most camps had a large balance at the end of the war due to the issue of items, food or clothing, being curtailed due to the 'retaliation' theory. Many were captured during warm months and didn't have hard weather gear on them. Most never got it.
The Cotton Exchange was to pay for clothing for prisoners and with that the war department stopped providing funds. The 'exchange' was a comedy of errors, real or manufactured I don't know for sure, and it did not do what it was supposed to. The 'looks good on paper theory' again.

Pam